Typescript中的`get`和`set`被称为访问器，它们是定义对象属性的特殊方法。`get`方法用于访问属性的值，而`set`方法用于设置属性的值。当你想要在读取或设置属性时加入额外逻辑时，这些方法特别有用。

下面是一个使用TypeScript中的`get`和`set`访问器的示例：

```typescript
class Person {
    private _firstName: string;
    private _lastName: string;

    constructor(firstName: string, lastName: string) {
        this._firstName = firstName;
        this._lastName = lastName;
    }

    // 使用get访问器来获取完整的名字
    get fullName(): string {
        return `${this._firstName} ${this._lastName}`;
    }

    // 使用set访问器来设置姓氏，并执行一些额外的逻辑，比如校验
    set lastName(name: string) {
        if (name.length > 0) {
            this._lastName = name;
        } else {
            console.error('Invalid last name');
        }
    }
}

let person = new Person('John', 'Doe');

// 通过get访问器获取fullName
console.log(person.fullName); // 输出：John Doe

// 通过set访问器修改姓氏
person.lastName = 'Smith';
console.log(person.fullName); // 输出：John Smith

// 尝试设置一个无效的姓氏
person.lastName = ''; // 输出：Invalid last name
```

在上面的例子中，我们定义了一个`Person`类，它有私有属性`_firstName`和`_lastName`。我们为这个类定义了两个访问器：

1. `get fullName()`：这个`get`访问器允许我们获取一个人的全名，它通过将`_firstName`和`_lastName`组合起来返回一个字符串。

2. `set lastName(name: string)`：这个`set`访问器允许我们设置一个人的姓氏。在设置姓氏之前，我们可以在这里加入验证逻辑，比如检查新姓氏是否为空，如果为空，则给出错误消息并拒绝更新。

通过使用`get`和`set`访问器，我们可以封装对象的内部状态，同时提供一个简洁的API来访问和修改这些状态，也可以增加验证或其他必要的逻辑。

How to use get and set in typescript?

在强制刷新或更新Service Worker时，通常涉及以下几个步骤：

1. **更新Service Worker文件**：
   确保你已经对Service Worker脚本做了修改。即便是很小的改动，如更新文件中的注释，也能触发Service Worker的更新事件，因为浏览器会检查Service Worker文件是否有字节级别的变化。

2. **Service Worker生命周期利用**：
   Service Worker的生命周期中有一个`install`事件。当检测到Service Worker文件有更新时，新的Service Worker将会进入`install`阶段。在这个阶段，你可以清除旧缓存并且执行新的缓存逻辑。

3. **激活新的Service Worker**：
   在新的Service Worker安装后，它会进入`wait`状态。你可以通过调用`self.skipWaiting()`方法来强制当前正在等待的Service Worker立即进入`activate`状态。

4. **更新客户端**：
   新的Service Worker激活后，并不会控制当前打开的页面，直到下次用户访问。为了让新的Service Worker立即接管，可以使用`clients.claim()`方法。

5. **通知用户**：
   如果你希望用户知道有一个新版本可用，并且鼓励他们刷新页面来使用新的Service Worker，可以在页面上显示一个通知或者按钮来提示用户。

### 示例代码

以下是一个简单的Service Worker更新流程实例：

```javascript
// 在Service Worker文件中
self.addEventListener('install', event => {
  // 强制当前正在等待的Service Worker立即进入activate状态
  self.skipWaiting();
});

self.addEventListener('activate', event => {
  // 让新的Service Worker立即接管当前页面
  event.waitUntil(clients.claim());
  // 清理旧版本缓存的逻辑
});
```

```javascript
// 在注册Service Worker的主文件中
if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/service-worker.js').then(reg => {
    reg.addEventListener('updatefound', () => {
      const newWorker = reg.installing;
      newWorker.addEventListener('statechange', () => {
        if (newWorker.state === 'installed' && navigator.serviceWorker.controller) {
          // 新的Service Worker已经就绪，可以通知用户刷新页面了
          // 这里可以显示一个“更新可用”的通知或者刷新按钮
        }
      });
    });
  });
}
```

### 强制刷新页面

如果你控制了页面逻辑，你甚至可以在新的Service Worker激活后自动刷新页面，但这通常不是一个好的做法，因为用户可能会丢失未保存的状态。

你可以这样做：

```javascript
if ('serviceWorker' in navigator) {
  navigator.serviceWorker.addEventListener('controllerchange', () => {
    // 当新的Service Worker取得控制权时，刷新页面
    window.location.reload();
  });
}
```

请注意，强制刷新页面可能导致用户体验问题，因此确保在适当的时机执行该操作，例如，当用户完成他们的工作并且页面可以安全地刷新时。

这些步骤和代码示例展示了如何在更新Service Worker时保持页面的正常运作并及时地将更新推送给用户。在实际应用中，会根据具体的业务需求和更新策略来调整这个流程。

As the previous answers stated, there is a 1 day (24hr) built-in limit for the browser to look for updates to the service worker, but what you need to be mindful of is you still need to call `.update()` on your `ServiceWorkerRegistration` object otherwise the original version of the file will be used.

While testing changes in Chrome, I always right-click on the refresh button and select 'Empty Cache and Hard Reset' (options are available when developer tools are open) when working on my service worker script.

'sw-precache' has been superseded by [Workbox](https://workboxjs.org/) which generates hashes for the files you want to precache and adds those to the source code of your service worker (I don't know if `sw-precache` works the same way, Jeff's answer suggests it does). If any of the files you want to precache change -- and you re-run your build -- the updated hashes in your service worker are updated which pretty much guarantees the service worker will be "at least one byte different".

When you reload (`ctrl-r`) or re-visit your app the browser will fetch again the service worker that was registered for it. And, if that service worker has changed, it will be "queued up" to manage the app. But it won't start managing the app until you close all tabs with the app open, and then open a new one.

When you hard refresh (`shift-ctrl-r`) [it’ll always load without a controller](https://github.com/w3c/ServiceWorker/blob/master/explainer.md#so-im-controlling-pages-now) which is not the same as using your new service worker.

For testing during development, I use [skip waiting](https://developers.google.com/web/fundamentals/primers/service-workers/lifecycle#skip_waiting) in devtools to make the new service worker replace the old one without waiting for me to close all the tabs.

If one file's hash changes, that's enough to ensure that the service worker JavaScript file generated by `sw-precache` changes. That, in turn, is enough to trigger the service worker update flow.

If you're not seeing an update flow triggered while testing things out, then it may be due to the service worker JavaScript file being served with HTTP caching headers that cause it to be fetched from the browser's cache rather than the from the network.

See [https://stackoverflow.com/a/38854905/385997](https://stackoverflow.com/a/38854905/385997) for a discussion of how HTTP caching headers come into play, and the best practices with regards to that.

One option that I have implemented from a UX standpoint is calling the unregister method on your service worker. ([https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration/unregister](https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration/unregister))

Once the unregister process is complete you can:

1.  force the window to refresh (window.location.reload)
2.  Based on your load up process, you can fetch the new service worker which will hopefully cache all your new content.

I have ran into weird issues with the service worker before, so this type of solution allows you to somewhat clear the old cache and refresh the state of your application without forcing users to clear their actual browser cache, while at the same time reloading your application.

EX (How to Unregister):

    serviceworker.unregister()
        .then( unregResult => { 
           //You can check if successful with Promise result 'unregResult'
           window.location.reload();
        })

Store a version number in `service‑worker.js`
=============================================

**A one-character change** in the controlling `service-worker.js` will automatically trigger a PWA update. Hence, if you store the version number in a `const` in this file and change it, an update of the PWA will be triggered.

How the update eventually is handled, is determined by the `service-worker.js`. Different update strategies may be defined in terms of the size and volatility of the PWA assets.

However, there is one **important caveat.** Make sure that the **browser cache expiry directive** set by the `.htaccess` file on your asset server is set to a really short duration (e.g. `hours`) or even to [**none**](https://stackoverflow.com/a/66756683/2192488). Failing to do so, will result in the browser not seeing any change for days to come in the `manifest.json`, nor the `service-worker.js`.

More details about service worker behaviour are available from [Google Web Fundamentals](https://developers.google.com/web/fundamentals/primers/service-workers/lifecycle).

当您希望建立一个新版本的 Service Worker 并替换掉旧版本时，您需要确保新的 Service Worker 可以被安装并且激活，从而更新用户的页面。这个过程通常涉及以下步骤：

1. **更新 Service Worker 文件：** 为了触发 Service Worker 的更新检查，你需要对 Service Worker 的脚本文件做出一些变化。浏览器会比较 Service Worker 文件的字节码来决定是否需要安装一个新版本。

2. **安装新的 Service Worker：** 当浏览器检测到 Service Worker 文件有变化时，它会尝试安装新的 Service Worker。安装过程通常在 `install` 事件中完成。

3. **等待新的 Service Worker 激活：** 默认情况下，新的 Service Worker 在安装后不会立即激活，因为旧的 Service Worker 可能还在控制着当前页面。新的 Service Worker 会处于 waiting 状态，直到当前所有的页面都关闭，它才会被激活。

4. **加速激活过程：** 如果您想要强制新的 Service Worker 立即接管，您可以在新的 Service Worker 中使用 `self.skipWaiting()`，这样它就可以跳过等待直接进入激活状态。

5. **更新客户端页面：** 一旦新的 Service Worker 激活，旧的客户端（页面）需要被更新。可以在新的 Service Worker 的 `activate` 事件中使用 `clients.claim()` 来实现。这将允许新的 Service Worker 立即控制所有客户端。

这里是一个简单的例子，展示了如何在 Service Worker 脚本中使用 `skipWaiting` 和 `clients.claim`：

```javascript
self.addEventListener('install', function(event) {
  // 执行安装步骤
  event.waitUntil(
    // 缓存资源等操作
    self.skipWaiting() // 强制进行 Service Worker 更新
  );
});

self.addEventListener('activate', function(event) {
  event.waitUntil(
    clients.claim() // 让新的 Service Worker 接管页面
  );
});
```

为了从页面脚本中强制刷新 Service Worker，你可以使用以下步骤：

1. 注册 Service Worker（如果尚未注册）。
2. 监听 Service Worker 的更新。
3. 当检测到更新时，可以用 `postMessage` API 发送消息给 Service Worker，要求其强制更新。

例如：

```javascript
if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/service-worker.js').then(reg => {
    reg.addEventListener('updatefound', () => {
      const newWorker = reg.installing;
      newWorker.addEventListener('statechange', () => {
        if (newWorker.state === 'installed' && navigator.serviceWorker.controller) {
          // 通知新的 Service Worker 接管控制权
          newWorker.postMessage({ action: 'SKIP_WAITING' });
        }
      });
    });
  });
}

// Service Worker 文件中
self.addEventListener('message', (event) => {
  if (event.data.action === 'SKIP_WAITING') {
    self.skipWaiting();
  }
});
```

这样，您就可以强制刷新/更新 Service Worker 了。记住，虽然可以强制更新 Service Worker，但最好还是确保这样做对用户来说是平滑且不会导致数据丢失的。

对于Service Worker的强制刷新或更新，以下是步骤和考虑事项：

1. **更新 Service Worker 文件**：
   要使浏览器检查更新的 Service Worker，你需要更改 Service Worker 文件 (`service-worker.js` 或任何你命名的文件) 的内容。即使是一个简单的空格或注释的变化，都会导致浏览器认为 Service Worker 已经更新。

2. **Service Worker 生命周期**：
   Service Worker 有一个内建的生命周期，用于管理安装和更新。当一个新的 Service Worker 被检测到，且与现有 Service Worker 不同时，它会进入 `install` 阶段，但不会立即控制页面，而是等待 `activate` 阶段。

3. **跳过等待（Skip Waiting）**：
   默认情况下，新的 Service Worker 会在等待状态，直到所有加载了旧 Service Worker 的页面关闭。为了让新的 Service Worker 立即接管，你可以在 Service Worker 文件中添加 `self.skipWaiting()`，这样新的 Service Worker 在安装结束后会立即进入激活状态。

    ```javascript
    // 在 Service Worker 的 'install' 事件中
    self.addEventListener('install', event => {
        event.waitUntil(
            // 强制进行更新
            self.skipWaiting()
        );
    });
    ```

4. **客户端的 Claim**：
   一旦激活，新的 Service Worker 应该开始接管控制页面。但是，如果你想让 Service Worker 立即控制所有客户端，包括加载旧 Service Worker 的页面，可以使用 `self.clients.claim()` 方法。

    ```javascript
    // 在 Service Worker 的 'activate' 事件中
    self.addEventListener('activate', event => {
        event.waitUntil(
            self.clients.claim()
        );
    });
    ```

5. **更新客户端页面**：
   即使新的 Service Worker 激活并开始控制页面，你也可能需要刷新页面，以确保新的 Service Worker 接管并应用新的缓存策略或其他更新。你可以通过以下方式通知用户刷新页面，或者在某些情况下可以强制刷新。

    ```javascript
    // 通常，你可以提醒用户重新加载页面
    if (navigator.serviceWorker) {
        navigator.serviceWorker.addEventListener('controllerchange', () => {
            // 在这里通知用户或刷新页面
            console.log('Service Worker 已更新。');
            window.location.reload();
        });
    }
    ```

6. **更新缓存**：
   更新了 Service Worker 后，你还需要更新缓存的资源。你可以在 `install` 事件中通过删除旧缓存的方式来做到这一点。

    ```javascript
    self.addEventListener('install', (event) => {
        event.waitUntil(
            caches.keys().then(cacheNames => {
                return Promise.all(
                    cacheNames.map(cache => {
                        if (cache !== currentCacheName) {
                            // 删除旧缓存
                            return caches.delete(cache);
                        }
                    })
                );
            })
        );
    });
    ```

通过使用以上技术，你可以确保 Service Worker 的更新能够快速且强制地推送到客户端，这对于紧急修复错误或推出新功能尤为重要。记住，Service Worker 的更新可能涉及对用户体验的中断，所以应该在用户不太可能被中断的时候进行更新，或者确保前端有相应的提醒和用户引导措施。

How to force service worker to update？

在TypeScript中，`get`和`set`访问器允许我们有效地封装对象中的属性，通过这种方式可以在读取或写入属性时执行额外的逻辑。`get`访问器用于定义如何读取属性值，而`set`访问器则定义如何设置属性值。下面是一个使用`get`和`set`访问器的例子：

```typescript
class Person {
    private _firstName: string;
    private _lastName: string;

    constructor(firstName: string, lastName: string) {
        this._firstName = firstName;
        this._lastName = lastName;
    }

    // 使用 get 访问器来读取 fullName
    get fullName(): string {
        return `${this._firstName} ${this._lastName}`;
    }

    // 使用 set 访问器来设置 firstName 和 lastName
    set fullName(name: string) {
        const parts = name.split(' ');
        if (parts.length !== 2) {
            throw new Error('请输入一个完整的名字，例如：John Doe');
        }
        this._firstName = parts[0];
        this._lastName = parts[1];
    }
}

let person = new Person('John', 'Doe');

// 通过 get 访问器获取 fullName
console.log(person.fullName); // 输出: John Doe

// 通过 set 访问器修改 fullName
person.fullName = 'Jane Smith';

// 再次通过 get 访问器获取修改后的 fullName
console.log(person.fullName); // 输出: Jane Smith
```

在上述例子中，`Person` 类有两个私有属性 `_firstName` 和 `_lastName`。为了能够控制对这些属性的访问，我们定义了一个 `fullName` 属性，它有一个 `get` 访问器和一个 `set` 访问器。

- `get fullName()` 方法用于在需要时构造并返回一个完整的名字，即 `_firstName` 和 `_lastName` 的组合。
- `set fullName(name: string)` 方法允许我们通过一个字符串来设置 `_firstName` 和 `_lastName`。如果传入的字符串不是两个部分组成，则会抛出错误。

这样，我们就可以用面向对象的方式，封装属性的具体实现细节，同时通过访问器提供简单的接口供外部代码使用。这样做的好处是可以在设置和获取属性时添加验证逻辑或其他附加操作，而不必暴露类的内部结构。

TypeScript uses getter/setter syntax that is like ECMAScript4/ActionScript3.

    class foo {
        private _bar: boolean = false;
        get bar(): boolean {
            return this._bar;
        }
        set bar(value: boolean) {
            this._bar = value;
        }
    }
    

However, in order to use it at all, you must make sure the TypeScript compiler targets ECMAScript5 or higher. If you are running the command line compiler, use `--target` flag like this:

    tsc --target ES5
    

If you are using Visual Studio, you must edit your project file to add the flag to the configuration for the TypeScriptCompile build tool. You can see that [here](https://stackoverflow.com/a/17261732/1733315):

That will produce this JavaScript, using the ECMAScript 5 `Object.defineProperty()` feature.

    var foo = (function () {
        function foo() {
            this._bar = false;
        }
        Object.defineProperty(foo.prototype, "bar", {
            get: function () {
                return this._bar;
            },
            set: function (value) {
                this._bar = value;
            },
            enumerable: true,
            configurable: true
        });
        return foo;
    })();
    

More recent versions of EcmaScript will produce code that looks more like the original TypeScript. For instance, targeting EcmaScript2017 will produce:

    "use strict";
    class foo {
        constructor() {
            this._bar = false;
        }
        get bar() {
            return this._bar;
        }
        set bar(value) {
            this._bar = value;
        }
    }
    

So to use it,

    var myFoo = new foo();
    if(myFoo.bar) {         // calls the getter
        myFoo.bar = false;  // calls the setter and passes false
    }
    

As @DanFromGermany suggests below, if you are simply reading and writing a local property like `foo.bar = true`, then having a setter and getter pair is overkill. You can always add them later if you need to do something, like logging, whenever the property is read or written.

Getters can be used to implement readonly properties. Here is an example that also shows how getters interact with readonly and optional types.

    //
    // type with optional readonly property.
    // baz?:string is the same as baz:string|undefined
    //
    type Foo = {
        readonly bar: string;
        readonly baz?: string;
    }
    const foo:Foo = {bar: "bar"}
    console.log(foo.bar) // prints 'bar'
    console.log(foo.baz) // prints undefined
    
    //
    // interface with optional readonly property
    //
    interface iFoo {
        readonly bar: string;
        readonly baz?: string;
    }
    
    const ifoo:iFoo = {bar: "bar"}
    console.log(ifoo.bar)  // prints 'bar'
    console.log(ifoo.baz)  // prints undefined
    
    
    //
    // class implements bar as a getter, 
    // but leaves off baz.
    //
    class iBarClass implements iFoo {
    
        get bar() { return "bar" }
    }
    const iBarInstance = new iBarClass()
    console.log(iBarInstance.bar) // prints 'bar'
    console.log(iBarInstance.baz) // prints 'undefined'
    // accessing baz gives warning that baz does not exist 
    // on iBarClass but returns undefined
    // note that you could define baz as a getter
    // and just return undefined to remove the warning.
    
    
    //
    // class implements optional readonly property as a getter
    //
    class iBazClass extends iBarClass {
        private readonly _baz?: string
    
        constructor(baz?:string) {
            super()
            this._baz = baz
        }
    
        get baz() { return this._baz; }
    }
    
    const iBazInstance = new iBazClass("baz")
    console.log(iBazInstance.bar)  // prints bar
    console.log(iBazInstance.baz)  // prints baz

Ezward has already provided a good answer, but I noticed that one of the comments asks how it is used. For people like me who stumble across this question, I thought it would be useful to have a link to the official documentation on getters and setters on the Typescript website as that explains it well, will hopefully always stay up-to-date as changes are made, and shows example usage:

[http://www.typescriptlang.org/docs/handbook/classes.html](http://www.typescriptlang.org/docs/handbook/classes.html)

In particular, for those not familiar with it, note that you don't incorporate the word 'get' into a call to a getter (and similarly for setters):

    var myBar = myFoo.getBar(); // wrong    
    var myBar = myFoo.get('bar');  // wrong
    

You should simply do this:

    var myBar = myFoo.bar;  // correct (get)
    myFoo.bar = true;  // correct (set) (false is correct too obviously!)
    

given a class like:

    class foo {
      private _bar:boolean = false;
    
      get bar():boolean {
        return this._bar;
      }
      set bar(theBar:boolean) {
        this._bar = theBar;
      }
    }
    

then the 'bar' getter for the private '\_bar' property will be called.

Here's a working example that should point you in the right direction:

    class Foo {
        _name;
    
        get Name() {
            return this._name;
        }
    
        set Name(val) {
            this._name = val;
        }
    }
    

Getters and setters in JavaScript are just normal functions. The setter is a function that takes a parameter whose value is the value being set.

You can write this

    class Human {
        private firstName : string;
        private lastName : string;
    
        constructor (
            public FirstName?:string, 
            public LastName?:string) {
    
        }
    
        get FirstName() : string {
            console.log("Get FirstName : ", this.firstName);
            return this.firstName;
        }
        set FirstName(value : string) {
            console.log("Set FirstName : ", value);
            this.firstName = value;
        } 
    
        get LastName() : string {
            console.log("Get LastName : ", this.lastName);
            return this.lastName;
        }
        set LastName(value : string) {
            console.log("Set LastName : ", value);
            this.lastName = value;
        } 
    
    }

I think I probably get why is it so confusing. In your example, we wanted getters and setters for `_name`. But we achieve that by creating getters and setters for an unrelated class variable `Name`.

Consider this:

    class Car {
        private tiresCount = 4;
        get yourCarTiresCount(){
            return this.tiresCount;
        }
        set yourCarTiresCount(count) {
            alert('You shouldn\'t change car tire count')
        }
    }
    

Above code does following:

1.  `get` and `set` create getter and setter for `yourCarTiresCount` (**not for `tiresCount`**).

The getter is :

    function () {
        return this.tiresCount;
    }
    

and the setter is :

    function (count) {
        alert('You shouldn\'t change car tire count');
    }
    

Meaning, every time we do `new Car().yourCarTiresCount`, getter runs. And for every `new Car().yourCarTiresCount('7')` setter runs.

2.  **Indirectly** create getter, but not the setter, for private `tireCount`.

How to use get and set in typescript

注册 Service Worker 可能会因为多种原因失败，以下是一些常见的原因及其解释：

### 1. 作用域问题（Scope）
Service Worker 的作用域由其注册时的位置决定。如果你尝试在子目录注册一个 Service Worker，而这个 Service Worker 的作用域是在更高级别的目录，那么注册可能会失败。例如，试图在 `/pages/` 下注册一个 Service Worker，但其作用域是 `/`，浏览器将不会允许这么做。

**例子**：
```javascript
// 假设在 /pages/index.html 中
navigator.serviceWorker.register('/service-worker.js', { scope: '/' })
.then(function(registration) {
  // 注册成功
})
.catch(function(error) {
  // 注册失败，可能是由于作用域问题
});
```

### 2. 路径错误
如果 Service Worker 文件的路径不正确，浏览器无法找到 Service Worker 脚本，也会导致注册失败。

**例子**：
```javascript
// 假设实际的 Service Worker 位于 /scripts/service-worker.js
navigator.serviceWorker.register('/wrong-path/service-worker.js')
.then(function(registration) {
  // 注册成功
})
.catch(function(error) {
  // 注册失败，因为路径不正确
});
```

### 3. 不支持 Service Worker
并非所有的浏览器都支持 Service Worker，尝试在不支持 Service Worker 的浏览器中注册它，自然会失败。

**例子**：
```javascript
if ('serviceWorker' in navigator) {
  // 浏览器支持 Service Worker
  navigator.serviceWorker.register('/service-worker.js')
  .then(function(registration) {
    // 注册成功
  })
  .catch(function(error) {
    // 注册失败
  });
} else {
  // 浏览器不支持 Service Worker
  console.log('Service Worker is not supported by this browser.');
}
```

### 4. 服务工作线程文件中的错误
如果 Service Worker 文件本身存在语法错误或其他问题，它的注册也会失败。

**例子**：
```javascript
// service-worker.js 文件中的语法错误
self.addEventListener('fetch', function(event) {
  // 缺少了闭合的花括号
```

### 5. HTTPS 协议
出于安全原因，Service Worker 只能在 HTTPS 协议下注册成功（除了本地环境，如 `localhost`，可以使用 HTTP）。如果你在非安全的 HTTP 环境下尝试注册 Service Worker，注册将失败。

**例子**：
```javascript
// 尝试在 HTTP 环境下注册 Service Worker
navigator.serviceWorker.register('/service-worker.js')
.then(function(registration) {
  // 注册成功
})
.catch(function(error) {
  // 注册失败，因为不是 HTTPS 环境
});
```

### 6. 浏览器隐私模式
某些浏览器在隐私模式下可能不允许使用 Service Worker，因此尝试在这种模式下注册可能会失败。

### 7. 过时的浏览器缓存
如果浏览器缓存了旧的 Service Worker 文件或注册代码，可能导致注册看似失败，这时候清除缓存可能会解决问题。

针对上述任何注册失败的情况，开发者都应该通过浏览器的开发者工具检查错误信息，以便找到具体的失败原因并解决。通常，注册失败时的 catch 代码块可以获取到错误信息，这对于调试非常有用。

Why service worker registration failed?

Service Worker 控制台通常指的是浏览器开发者工具中与 Service Worker 相关的部分，它允许开发者管理、调试和了解 Service Worker 的状态和行为。Service Worker 是一种运行在浏览器背后、独立于网页的 JavaScript Worker，它可以用来处理离线缓存、推送通知和背景数据同步等功能。

在 Google Chrome 浏览器中，可以通过以下步骤访问 Service Worker 控制台：

1. 打开 Chrome 浏览器。
2. 访问一个使用了 Service Worker 的网站。
3. 右键点击页面，选择“检查”（Inspect），或者使用快捷键`Ctrl+Shift+I`（Windows/Linux）或`Cmd+Opt+I`（Mac）来打开开发者工具。
4. 在开发者工具窗口中，选择“Application”面板。
5. 在“Application”面板的左侧菜单中，找到并点击“Service Workers”。

在这个部分，你可以看到当前网站注册的所有 Service Workers 的信息，包括它们的状态（激活、运行中、停止）、作用域（scope）、以及是否处于调试状态。此外，你还可以对 Service Workers 进行一些操作，比如更新、停止或者删除 Service Worker，或者模拟离线状态来测试 Service Worker 的离线行为。

例如，如果我为我的网站开发了一个 Service Worker 来缓存静态资源，当用户第一次访问网站时，Service Worker 会被安装并激活，之后它会根据预定义的缓存策略缓存一些静态资源。当用户在没有网络连接的情况下再次访问网站时，即使处于离线状态，网站依然可以通过 Service Worker 提供那些已经缓存的资源，从而提升用户体验。

总的来说，Service Worker 控制台是 Chrome 开发者工具中一个非常有用的部分，它为开发者提供了强大的功能来管理和调试 Service Worker。

Go to chrome://serviceworker-internals

Choose any service worker and start it if not already started.

Click on Inspect!!

Boom! You have the console there!

If a page has a service worker, then that service worker's logs show in that page's JavaScript console. You can see the source of a log line on the right-hand side of the log:

[![log line sources](https://i.stack.imgur.com/aKNa3.png)](https://i.stack.imgur.com/aKNa3.png)

In the console, there is a select box to select the _JavaScript context_. This defaults to `top` (which means "show everything"), but you can select a more specific context for just the service worker:

[![selecting alternative context](https://i.stack.imgur.com/HhTQx.png)](https://i.stack.imgur.com/HhTQx.png)

Service Worker 控制台通常指的是开发者工具中与 Service Worker 相关的部分，它可以让开发者查看和管理 Service Workers 的状态、生命周期、以及相关的事件和数据。Service Worker 是一种运行在浏览器背后的脚本，它可以帮助实现离线体验、消息推送和背景同步等功能。

要在 Chrome 浏览器中找到与 Service Worker 相关的控制台，您可以按照以下步骤操作：

1. 打开 Chrome 浏览器。
2. 访问您想要检查 Service Worker 的网站。
3. 点击右上角的三个点按钮，选择“更多工具”，然后在下拉菜单中选择“开发者工具”。也可以直接使用快捷键 `Ctrl+Shift+I`（Windows/Linux）或 `Cmd+Option+I`（Mac）来打开开发者工具。
4. 在开发者工具窗口中，点击上方的“Application”（应用）标签。如果看不到“Application”，可能需要点击“>>”符号来展开隐藏的标签列表。
5. 在左侧的导航栏中，找到并点击“Service Workers”选项。在这里，您可以看到当前活动的 Service Workers，包括它们的状态、脚本URL、是否被控制的页面等信息。
6. 在“Service Workers”选项下，您可以看到诸如“Offline”（离线模式）、“Update on reload”（重新加载时更新）等选项，这些选项可以帮助测试和调试 Service Workers。

例如，如果您正在开发一个支持离线功能的网页应用，您可能会在 Service Worker 中编写代码来缓存某些资源。然后，您可以在 Service Worker 控制台中模拟离线状态，来测试您的网页在没有网络连接时是否能够正确地从缓存中加载资源。

这些工具对于开发者来说非常有用，因为它们可以帮助确保 Service Workers 正确安装、激活、运行，并且能够处理各种事件，从而提升网页应用的性能和用户体验。

Service Worker 控制台是开发者工具（Developer Tools）的一部分，是 Google Chrome 浏览器提供的一个界面，用于检查和管理网页或应用中的 Service Workers。Service Worker 是一种运行在浏览器背后的脚本，可以帮助实现离线体验、消息推送和背景同步等功能。它作为一个独立的线程运行，不依赖于网页直接控制，因此可以在不打开网页的情况下执行任务。

在 Chrome 浏览器中，您可以通过以下步骤访问 Service Worker 控制台：

1. 打开 Chrome 浏览器。
2. 访问您想要检查的网站。
3. 右键点击页面，选择“检查”（或使用快捷键 Ctrl+Shift+I / Cmd+Option+I 打开开发者工具）。
4. 在开发者工具中，切换到“Application”选项卡。
5. 在左侧导航菜单中，找到并展开“Service Workers”部分。

在这里，您可以看到当前域下注册的所有 Service Workers 的详细信息，包括它们的状态（例如，已激活、正在运行或已停止）、作用域、脚本URL、以及是否被控制的页面。您还可以对 Service Workers 进行管理，例如更新、卸载、启用离线功能或者调试 Service Workers。

例如，如果我在开发一个渐进式网络应用（PWA），我会使用 Service Worker 来缓存关键资产，以确保我的应用即使在离线状态下也能提供核心功能。在实施缓存策略后，我会通过 Service Worker 控制台检查 Service Worker 的状态，确保它已正确注册并激活，以及验证缓存行为是否符合预期。

What is service worker console and where is it in chrome browser?

在页面刷新时激活更新后的service worker，通常涉及以下几个步骤：

1. **注册Service Worker：**
   首先，需要在你的网页中注册service worker。这通常在JavaScript的主文件中进行：

   ```javascript
   if ('serviceWorker' in navigator) {
     window.addEventListener('load', function() {
       navigator.serviceWorker.register('/service-worker.js').then(function(registration) {
         // 注册成功
         console.log('ServiceWorker registration successful with scope: ', registration.scope);
       }, function(err) {
         // 注册失败
         console.log('ServiceWorker registration failed: ', err);
       });
     });
   }
   ```

2. **更新Service Worker文件：**
   当你更新了service worker的JavaScript文件（`service-worker.js`），浏览器会检测到文件内容的变化，这时候新的service worker会开始安装流程，但此时不会立即激活。

3. **Install和Activate事件：**
   在service worker文件内部，你可以监听`install`和`activate`事件。新的service worker在安装后通常会进入等待状态，直到所有的客户端（页面）都关闭，然后才会被激活。

   ```javascript
   self.addEventListener('install', event => {
     // 执行安装步骤
   });

   self.addEventListener('activate', event => {
     // 在激活时，通常会清理旧的缓存等
     event.waitUntil(
       // 清理工作
     );
   });
   ```

4. **立即激活新的Service Worker：**
   若要在页面刷新时立即激活新的service worker，可以利用`self.skipWaiting()`方法。在`install`事件中调用这个方法可以使新的service worker跳过等待阶段，直接进入激活状态。

   ```javascript
   self.addEventListener('install', event => {
     event.waitUntil(
       // 安装步骤例如缓存文件等，
       // 然后调用skipWaiting来立即激活service worker
       self.skipWaiting()
     );
   });
   ```

5. **控制页面：**
   即使service worker已经激活，如果页面在安装新的service worker之前就已经打开了，那么你还需要通过`clients.claim()`在activate事件中获取对其控制权。

   ```javascript
   self.addEventListener('activate', event => {
     event.waitUntil(
       clients.claim() // 这个操作会使新的service worker立即控制所有的页面
     );
   });
   ```

6. **页面刷新：**
   你可以在页面上提供一个机制来刷新页面，或者通过service worker通知用户，并使用`window.location.reload()`来刷新页面以使用更新后的service worker。

   ```javascript
   navigator.serviceWorker.addEventListener('controllerchange', () => {
     window.location.reload();
   });
   ```

7. **确保更新的Service Worker被应用：**
   对于已经打开的页面，为了立即应用新的service worker，你可能需要提醒用户刷新页面，或者使用前面提到的`window.location.reload()`强制刷新。

通过以上步骤，页面刷新后，更新后的service worker可以被激活并立即开始控制页面。不过，请注意，强制刷新用户的页面可能会导致用户体验不佳，因此应当谨慎使用。

There are conceptually two kinds of updates, and it isn't clear from your question which we're talking about, so I'll cover both.

Updating content
================

Eg:

*   The text of a blog post
*   The schedule for an event
*   A social media timeline

These will likely be stored in the cache API or IndexedDB. These stores live independently of the service worker - updating the service worker shouldn't delete them, and updating them shouldn't require an update to the service worker

Updating the service worker is the native equivalent of shipping a new binary, you shouldn't need to do that to (for example) update an article.

When you update these caches is entirely up to you, and they aren't updated without you updating them. I cover a number of patterns in the [offline cookbook](https://jakearchibald.com/2014/offline-cookbook/), but [this is my favourite one](https://jakearchibald.com/2014/offline-cookbook/#cache-then-network):

1.  Serve page shell, css & js from a cache using the service worker.
2.  Populate page with content from the cache.
3.  Attempt to fetch content from the network.
4.  If the content is fresher than what you have in the cache, update the cache and the page.

In terms of "update the page", you need to do that in a way that isn't disruptive to the user. For chronological lists this is pretty easy, as you just add the new stuff to the bottom/top. If it's updating an article it's a bit trickier, as you don't want to switch text from underneath the user's eyes. In that case it's often easier to show some kind of notification like "Update available - **show update**" which, when clicked, refreshes the content.

[Trained to thrill](https://jakearchibald.github.io/trained-to-thrill/) (perhaps the first ever service worker example) demonstrates how to update a timeline of data.

Updating the "app"
==================

This is the case where you _do_ want to update the service worker. This pattern is used when you're:

*   Updating your page shell
*   Updating JS and/or CSS

If you want the user to get this update in a non-atomic, but fairly safe way, there are patterns for this too.

1.  Detect updated service worker "waiting"
2.  Show notification to user "Update available - **update now**"
3.  When the user clicks this notification, postmessage to the service worker, asking it to call `skipWaiting`.
4.  Detect the new service worker becoming "active"
5.  `window.location.reload()`

Implementing this pattern is part of my [service worker Udacity course](https://www.udacity.com/course/offline-web-applications--ud899), and [here's the diff of the code before/after](https://github.com/jakearchibald/wittr/compare/task-update-notify...update-interaction).

You can take this further too. For example, you could employ some kind of semver-esque system, so you know the version of the service worker the user currently has. If the update is minor you may decide calling `skipWaiting()` is totally safe.

I wrote a blog post explaining how to handle this. [https://redfin.engineering/how-to-fix-the-refresh-button-when-using-service-workers-a8e27af6df68](https://redfin.engineering/how-to-fix-the-refresh-button-when-using-service-workers-a8e27af6df68)

I also have a working sample on github. [https://github.com/dfabulich/service-worker-refresh-sample](https://github.com/dfabulich/service-worker-refresh-sample)

There are four approaches:

1.  **`skipWaiting()` on installation.** This is dangerous, because your tab can get a mix of old and new content.
2.  **`skipWaiting()` on installation, and refresh all open tabs on `controllerchange`** Better, but your users may be surprised when the tab randomly refreshes.
3.  **Refresh all open tabs on `controllerchange`; on installation, prompt the user to `skipWaiting()` with an in-app "refresh" button.** Even better, but the user has to use the in-app "refresh" button; the browser's refresh button still won't work. This is documented in detail in [Google's Udacity course on Service Workers](https://www.udacity.com/course/offline-web-applications--ud899) and the [Workbox Advanced Guide](https://developers.google.com/web/tools/workbox/guides/advanced-recipes#offer_a_page_reload_for_users), as well as the `master` branch of my [sample on Github](https://github.com/dfabulich/service-worker-refresh-sample).
4.  **Refresh the last tab if possible.** During fetches in `navigate` mode, count open tabs ("clients"). If there's just one open tab, then `skipWaiting()` immediately and refresh the only tab by returning a blank response with a `Refresh: 0` header. You can see a working example of this in the `refresh-last-tab` branch of my [sample on Github](https://github.com/dfabulich/service-worker-refresh-sample/tree/refresh-last-tab).

Putting it all together...

In the Service Worker:

    addEventListener('message', messageEvent => {
        if (messageEvent.data === 'skipWaiting') return skipWaiting();
    });
    
    addEventListener('fetch', event => {
        event.respondWith((async () => {
            if (event.request.mode === "navigate" &&
            event.request.method === "GET" &&
            registration.waiting &&
            (await clients.matchAll()).length < 2
            ) {
                registration.waiting.postMessage('skipWaiting');
                return new Response("", {headers: {"Refresh": "0"}});
            }
            return await caches.match(event.request) ||
            fetch(event.request);
        })());
    });
    

In the page:

    function listenForWaitingServiceWorker(reg, callback) {
        function awaitStateChange() {
            reg.installing.addEventListener('statechange', function () {
                if (this.state === 'installed') callback(reg);
            });
        }
        if (!reg) return;
        if (reg.waiting) return callback(reg);
        if (reg.installing) awaitStateChange();
        reg.addEventListener('updatefound', awaitStateChange);
    }
    
    // reload once when the new Service Worker starts activating
    var refreshing;
    navigator.serviceWorker.addEventListener('controllerchange',
        function () {
            if (refreshing) return;
            refreshing = true;
            window.location.reload();
        }
    );
    function promptUserToRefresh(reg) {
        // this is just an example
        // don't use window.confirm in real life; it's terrible
        if (window.confirm("New version available! OK to refresh?")) {
            reg.waiting.postMessage('skipWaiting');
        }
    }
    listenForWaitingServiceWorker(reg, promptUserToRefresh);

In addition to Dan's answer;

**1\. Add the `skipWaiting` event listener in the service worker script.**

In my case, a CRA based application I use [cra-append-sw](https://github.com/bbhlondon/cra-append-sw) to add this snippet to the service worker.

> **Note:** if you are using a recent version of `react-scripts`, the snippet below is [automatically added](https://github.com/GoogleChrome/workbox/issues/2394) and you won't need to use `cra-append-sw`.

    self.addEventListener('message', event => {
      if (!event.data) {
        return;
      }
    
      if (event.data === 'SKIP_WAITING') {
        self.skipWaiting();
      }
    });
    

**2\. Update register-service-worker.js**

For me, it felt natural to reload the page when the user navigates within the site. In the register-service-worker script I've added the following code:

    if (navigator.serviceWorker.controller) {
      // At this point, the old content will have been purged and
      // the fresh content will have been added to the cache.
      // It's the perfect time to display a "New content is
      // available; please refresh." message in your web app.
      console.log('New content is available; please refresh.');
    
      const pushState = window.history.pushState;
    
      window.history.pushState = function () {
        // make sure that the user lands on the "next" page
        pushState.apply(window.history, arguments);
    
        // makes the new service worker active
        installingWorker.postMessage('SKIP_WAITING');
      };
    } else {
    

Essentially we hook into the native `pushState` function so we know that the user is navigating to a new page. Although, if you also use filters in your URL for a products page, for example, you may want to prevent reloading the page and wait for a better opportunity.

Next, I'm also using Dan's snippet to reload all tabs when the service worker controller changes. This also will reload the active tab.

      .catch(error => {
        console.error('Error during service worker registration:', error);
      });
    
    navigator.serviceWorker.addEventListener('controllerchange', () => {
      if (refreshing) {
        return;
      }
    
      refreshing = true;
      window.location.reload();
    });

Even though the OP has disagreed with skipWaiting, skipWaiting is actually the correct solution for many apps, especially single page apps.

Open your precache in DevTools, check if there are any lazy loaded files. If there aren't - meaning everything in your precache are fetched immediately on page load, then it's safe to call skipWaiting, which will delete the old precache, replace with new assets (including the new index.html), waiting to be served on the next refresh. Since all the old assets are already in memory, which are running with the old index.html, there's nothing wo worry about.

(If you see a file in the precache but you aren't sure whether it's downloaded on page load, reload and watch the network traffic in DevTools yourself)

If you do have lazy loaded assets, then it indeed could cause a problem, but that's not a new problem created by service worker. Imagine your user opened a tab, then you deploy a new version, then the user clicks something which triggers a lazy load, but that asset is no longer on your server. This is an old problem. Precache unintentionally solved this problem, but you shouldn't rely on it, instead you should have your own exception handling logic, unless your app was designed to leverage the precache from the very beginning.

How to activate updated service worker on refresh

Service Worker 的作用域（Scope）定义了它能够控制的内容范围，即 Service Worker 可以拦截和处理哪些请求。作用域是通过 Service Worker 注册时指定的，一般来说，Service Worker 只能控制其注册所在路径和下级路径的请求。

例如，如果您在 `/app/` 路径下注册了一个 Service Worker，它的作用域将被限制在 `/app/` 及其子路径下。这意味着，Service Worker 可以拦截 `/app/`、`/app/home`、`/app/settings` 等路径的请求，但它无法控制 `/` 根路径或 `/other` 路径下的请求。

这个作用域的限定有助于确保 Service Worker 不会影响到其它不相关的页面和应用，提供了一种安全的方式来限制 Service Worker 的控制范围。

举个例子，如果一个在线商城网站在其根目录下注册了 Service Worker，并设置了根目录为作用域，那么这个 Service Worker 将能控制商城网站的所有页面。然而，如果商城网站希望仅仅对产品目录页面使用 Service Worker 来缓存和提供离线支持，那么它可以单独在 `/products/` 路径下注册一个 Service Worker，将作用域限制在这个子目录中。这样，Service Worker 只会影响 `/products/` 路径下的请求，而不会影响到其他页面。

Service workers are basically a proxy between your web application and the internet, so it can intercept calls to the network if so desired.

Scope in this instance refers to the path that the service worker will be able to intercept network calls from. The `scope` property can be used explicitly define the scope it will cover. However:

Service workers can only intercept requests originating in the scope of the current directory that the service worker script is located in and its subdirectories. [Or as MDN states](https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API/Using_Service_Workers#Why_is_my_service_worker_failing_to_register):

> The service worker will only catch requests from clients under the service worker's scope.
> 
> The max scope for a service worker is the location of the worker.

As your service worker is located in `/static/mod/practice/`, it's not allowed to set its scope to `/practice/foopage/`. Requests to other hosts, e.g. `https://stackoverflow.com/foo`, can be intercepted in any case.

The easiest way to ensure that your service worker can intercept all the calls it needs to, would be to place it in the root directory of your web app (`/`). You can also override the default restrictions using an http header and manually setting the scope (see Ashraf Sabry's answer).

Leave the service worker file in whatever directory imposed by your project structure and set the `scope` option to `/` and add the `Service-Worker-Allowed` HTTP header to the response of your service worker file.

I'm using IIS, so I would add the following to web.config file:

    <location path="static/mod/practice/service-worker.js">
        <system.webServer>
            <httpProtocol>
                <customHeaders>
                    <add name="Service-Worker-Allowed" value="/" />
                </customHeaders>
            </httpProtocol>
        </system.webServer>
    </location>
    

And register the worker by:

    navigator.serviceWorker.register('/static/mod/practice/service-worker.js', { scope: '/' })
            .then(function (registration)
            {
              console.log('Service worker registered successfully');
            }).catch(function (e)
            {
              console.error('Error during service worker registration:', e);
            });
    

Tested on Firefox and Chrome.

Refer to the examples in [Service worker specification](https://w3c.github.io/ServiceWorker/#service-worker-script-response)

For the people who are using nginx it couldn't be any simpler:

    # Given that /static is your route to assets
    location /static {
            # using / as root scope
            add_header Service-Worker-Allowed /;
    ....

Just in case if the scope changes between development & production environment, as often we use local subdirectories for projects, using "./" for the scope may save the day (& make it dynamic).

    navigator.serviceWorker.register(
        `./service-worker.js`, 
        {
            scope: `./`
        }
    );

How to understanding service worker scope?

Service Worker 在 React JS 中是一个运行在浏览器背后的脚本，它不依赖于网页而独立工作，能够为应用提供不依赖网络的特性，比如离线内容的访问、背景同步和推送通知等。它相当于一个位于浏览器与网络之间的代理，可以截获和处理网络请求，以及根据需求管理缓存。

Service Worker 在 React 应用中的一个典型用途是创建渐进式网络应用（PWA）。PWA 是一种通过网络技术构建的应用程序，它可以提供类似原生应用的用户体验。通过使用 Service Worker，React 应用可以在用户的设备上缓存应用的核心文件，这样即使在没有网络连接的情况下，用户也能加载应用的基本界面和功能。

一个实际的例子是，当开发者使用 `create-react-app` 工具新建一个 React 项目时，生成的模板项目中自带了 Service Worker 的配置。这个配置默认是不启用的，但是开发者可以选择启用它，并根据实际需要对其进行配置，从而让应用具备 PWA 的特性。

启用 Service Worker 后，当用户首次访问 React 应用时，Service Worker 被安装并开始缓存应用的资源，如 HTML、CSS、JavaScript 文件和图片等。当用户再次访问该应用时，即使在离线状态下，Service Worker 也可以通过拦截请求并提供缓存的资源来加载应用。

Service Worker 还允许开发者通过编程方式精细控制缓存策略，例如决定哪些资源需要缓存、何时更新缓存、如何响应资源请求等。通过这种方式，可以优化应用的性能并提高用户体验。

You may not need a service worker for your application. If you are creating a project with create-react-app it is invoked by default

Service workers are well explained in this **[article](https://developers.google.com/web/fundamentals/primers/service-workers/)**. To Summarise from it

> A `service worker` is a script that your browser runs in the background, separate from a web page, opening the door to features that don't need a web page or user interaction. Today, they already include features like `push notifications` and `background sync` and have `ability to intercept and handle network requests`, including `programmatically managing a cache of responses`.
> 
> In the future, service workers might support other things like `periodic sync` or `geofencing`.

According to this **[PR to create-react-app](https://github.com/facebook/create-react-app/pull/1728)**

> `Service workers` are introduced with create-react-app via `SWPrecacheWebpackPlugin`.
> 
> Using a server worker with a cache-first strategy offers performance advantages, since the network is no longer a bottleneck for fulfilling navigation requests. It does mean, however, that developers (and users) will only see deployed updates on the "N+1" visit to a page, since previously cached resources are updated in the background.

The call to `register service worker` is enabled by default in new apps but you can always remove it and then you’re back to regular behaviour.

**In simple and plain words, it’s a script that browser runs in the background and has whatsoever no relation with web pages or the DOM, and provide out of the box features. It also helps you cache your assets and other files so that when the user is offline or on slow network.**

_Some of these features are proxying network requests, push notifications and background sync. Service workers ensure that the user has a rich offline experience._

You can think of the service worker as someone who sits between the client and server and all the requests that are made to the server pass through the service worker. Basically, a middle man. Since all the request pass through the service worker, it is capable to intercept these requests on the fly.

[![enter image description here](https://i.stack.imgur.com/ldRJk.png)](https://i.stack.imgur.com/ldRJk.png)

I'd like to add 2 important considerations about Service Workers to take into account:

1.  Service Workers require HTTPS. But to enable local testing, this restriction doesn't apply to `localhost`. This is for security reasons as a Service Worker acts like a _man in the middle_ between the web application and the server.
    
2.  With **Create React App** Service Worker is only enabled in the production environment, for example when running `npm run build`.
    

Service Worker is here to help developing a [Progressive Web App](https://web.dev/what-are-pwas/). A good resource about it in the context of Create React App can be found in their website [here](https://create-react-app.dev/docs/making-a-progressive-web-app/).

What is service worker in react js?

Service Worker 本身并不提供存储功能，但它常常与浏览器中的缓存 API 配合使用，来缓存应用资源。Service Worker 的缓存容量并不是由 Service Worker API 本身强制规定的，而是取决于浏览器的实现和用户设备的可用空间。

每个浏览器可能有不同的存储限制政策，并且这些政策可能会随着时间而改变。大多数现代浏览器都采用启发式方法动态管理每个原始站点（origin）的存储限额。通常，浏览器允许单个原始站点使用的存储量在几十到几百兆字节之间，这取决于用户设备上的总可用空间。

例如，Chrome 浏览器为所有网站的存储限制提供了一个动态配额，它通常是基于每个原始站点可用磁盘空间的一部分。这一部分可能在总磁盘空间的2-5%之间，但这个数字是不固定的，并且可能会根据不同的设备和用户的存储使用情况而变化。

为了给您一个实际的例子，假设用户设备上的可用空间为100GB，Chrome可能会为一个原始站点分配2GB作为最大存储限额。但请记住，这个限额是动态计算的，用户的存储使用情况和浏览器的策略会影响这个值。

总的来说，Service Worker 的缓存大小限制并不是固定不变的，它受多种因素影响，包括浏览器实现、设备存储容量、其他网站的存储使用情况等。开发者可以通过浏览器的配额管理 API 来检查可用存储量，并相应地管理缓存策略。

**Update Jan 15 2018**

The [StorageManager](https://developer.mozilla.org/en-US/docs/Web/API/StorageManager) interface of Storage API is becoming a standard for all storage related api queries. As mentioned by [@miguel-lattuada](https://stackoverflow.com/a/46933005/1657018), the [estimate API](https://developer.mozilla.org/en-US/docs/Web/API/StorageManager/estimate) would provide an estimate of the storage used a web app the available storage. Also, note the [QuotaExceededError](https://developer.mozilla.org/en-US/docs/Web/API/DOMException#exception-QuotaExceededError) exception which would help us in handling error scenarios.

eg code:

    if ('storage' in navigator && 'estimate' in navigator.storage) {
      navigator.storage.estimate().then(({usage, quota}) => {
        console.log(`Using ${usage} out of ${quota} bytes.`);
      }).catch(error => {
        console.error('Loading storage estimate failed:');
        console.log(error.stack);
      });
    } else {
      console.error('navigator.storage.estimate API unavailable.');
    }

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For more info, refer the following 2 great articles:

*   [MDN Web docs - Storage API](https://developer.mozilla.org/en-US/docs/Web/API/Storage_API)
*   [Google Developers: Estimating Available Storage Space](https://developers.google.com/web/updates/2017/08/estimating-available-storage-space)

* * *

**March 16 2017 (keeping it just for reference/history)**

Recently I came across this article: [offline-cookbook](https://jakearchibald.com/2014/offline-cookbook/#cache-persistence) which states as below:

Your **origin is given a certain amount of free space** to do what it wants with. That **free space is shared between all origin storage**: LocalStorage, IndexedDB, Filesystem, and of course Caches.

The **amount you get isn't spec'd**, it will differ depending on device and storage conditions. You can find out how much you've got via:

    navigator.storageQuota.queryInfo("temporary").then(function(info) {
       console.log(info.quota);
       // Result: <quota in bytes>
       console.log(info.usage);
       // Result: <used data in bytes>
    });
    

The above code [might not work in all the browsers](https://developer.mozilla.org/en-US/docs/Web/API/StorageQuota). (for eg: in chrome<48 one might have to look for webkitPersistentStorage etc)

**Other useful info/resources**

1.  As per [Offline Storage for Progressive Web Apps](https://medium.com/dev-channel/offline-storage-for-progressive-web-apps-70d52695513c#.19w8r1c4o) by Addy Osmani
    
    In `Chrome and Opera`: Your storage is per origin (rather than per API). Both storage mechanisms will store data until the browser quota is reached. Apps can check how much quota they’re using with the Quota Management API (as described above).
    
    `Firefox` no limits, but will prompt after 50MB data stored
    
    `Mobile Safari` 50MB max
    
    `Desktop Safari` unlimited (prompts after 5MB)
    
    `IE10+` maxes at 250MB and prompts at 10MB
    
2.  A more detailed guide on [Working with quota on mobile browsers](https://www.html5rocks.com/en/tutorials/offline/quota-research/) by Eiji Kitamura.
    

For now these are the most relevant articles/solutions found for my problem. If anyone knows some better article or specifications please share.

There's no explicit limit. All modern browsers are multi-process or similar, so a badly-designed page (or SW) won't do anything worse than crash itself.

Note that the SW spec is very explicit about the browser being able to kill and restart the SW at any time, for any reason. (If DevTools is open on a page, Chrome purposely kills SWs for the page constantly, to encourage you to adopt good practices.)

On latests browser you can use [StorageManager](https://developer.mozilla.org/en-US/docs/Web/API/StorageManager) which is an implementation of a new standard for browser storage, take a look at [this](https://developer.mozilla.org/en-US/docs/Web/API/Storage_API) mozilla article.

    let _storageStats = await navigator.storage.estimate();
    console.log(_storageStats);
    /*
      Will prompt something like this
      {quota: 15946471833, usage: 682}
      Which is a representation of quota/usage in bytes
      As you can see I get an insane quota of almost 16 GB
    */

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More info about `navigator.storage.estimate()` and `navigator.webkitTemporaryStorage.queryUsageAndQuota()` is here [https://developers.google.com/web/updates/2017/08/estimating-available-storage-space](https://developers.google.com/web/updates/2017/08/estimating-available-storage-space)

Testing page is here [https://thimbleprojects.org/startpolymer/361372/](https://thimbleprojects.org/startpolymer/361372/)

What is the storage limit for a service worker?

在 Progressive Web Application (PWA) 中，Service Worker 是一种运行在浏览器后台的脚本，负责管理缓存以及使应用能够在离线时工作。更新 Service Worker 管理的文件通常遵循以下流程：

### 文件更新流程：

1. **安装 Service Worker**：
   当用户首次访问 PWA 或者 Service Worker 文件 (`service-worker.js`) 有更新时，浏览器会尝试安装新的 Service Worker。这时，Service Worker 的 `install` 事件被触发。

2. **缓存新文件**：
   在 `install` 事件的处理函数中，通常会编写代码来打开缓存，并使用 `cache.addAll()` 方法缓存一个文件列表。此时，可以决定需要缓存哪些新文件或更新的文件。

3. **激活新的 Service Worker**：
   安装完成后，新的 Service Worker 会进入 `waiting` 状态。当网站上没有任何页面使用旧的 Service Worker 时，新的 Service Worker 会接收到 `activate` 事件。在 `activate` 事件的处理函数中，通常会清理旧缓存。

4. **管理旧缓存**：
   在激活阶段，可以通过比较缓存的版本来决定是否删除旧缓存中的文件，或者是整个旧缓存。这是通过 `caches.delete` 方法实现的。

5. **更新完成**：
   一旦新的 Service Worker 被激活并且旧缓存被清理，新的缓存开始生效，之后的网络请求都将通过新的 Service Worker 来处理。通过这个方式，文件得以更新。

### 何时更新：

- **Service Worker 文件变更**：
  每次用户访问 PWA 时，浏览器都会检查 Service Worker 文件是否有变更。如果检测到文件内容有一字节的改动，浏览器会认为 Service Worker 更新了，并开始上述的安装过程。

- **开发者触发更新**：
  开发者可以通过更改 Service Worker 文件，例如更新缓存文件的列表、修改缓存策略等来触发更新。开发者也可以通过版本号的方式来控制缓存的更新。

- **用户清空浏览器缓存**：
  如果用户清空了浏览器缓存，下次访问时 Service Worker 将会重新安装，意味着文件必须重新缓存。

### 示例：

在 Service Worker 的安装阶段，一个常见的更新文件的例子如下：

```javascript
const CACHE_NAME = 'cache-v1';
const URLS_TO_CACHE = [
  '/',
  '/styles/main.css',
  '/script/main.js'
];

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME)
    .then((cache) => {
      console.log('Opened cache');
      return cache.addAll(URLS_TO_CACHE);
    })
  );
});

self.addEventListener('activate', (event) => {
  const cacheWhitelist = [CACHE_NAME];
  event.waitUntil(
    caches.keys().then((cacheNames) => {
      return Promise.all(
        cacheNames.map((cacheName) => {
          if (cacheWhitelist.indexOf(cacheName) === -1) {
            return caches.delete(cacheName);
          }
        })
      );
    })
  );
});
```

在这个示例中，我们定义了一个缓存名称和需要缓存的文件列表。在 `install` 事件中，我们打开指定的缓存并添加了需要的文件。在 `activate` 事件中，我们移除了不在白名单中的所有旧缓存。这样，当 Service Worker 文件更新后，新的缓存策略就会生效，旧的文件被更新。

**No cache scenario (No Service worker):** Your PWA app will be cached only when you use Service worker. Manifest.json will help adding your web app to home screen with a icon and open without address bar. If you don't have a service worker or if your browser don't support it, web page will be loaded fresh every single time. No Cache.

**Cache-On Scenario (With Service worker):** Assuming you have service workers configured, service workers can cache by lazy loading or prefetching the files that are configured for caching (You can include or exclude caching anything from html, CSS, images to JSON/XML API responses).

After the initial cache, service worker will use the cache to serve your apps network request based on [cache approach](https://developers.google.com/web/ilt/pwa/caching-files-with-service-worker) you have implemented from below ones.

*   cache falling back to network
*   Network falling back to cache
*   Cache then network

Most apps choose to [precache](https://github.com/GoogleChromeLabs/sw-precache) due to performance benefits and look for new files on loading, if any changes found will be loaded on next session or prompt user to refresh. With this solution, each file will have a long Hash string for each file cached by service worker. On load of each application, hash code from server will be fetched to match and find what file needs to be updated and the same will be updated in a separate service worker thread. You can notice this in network tab -> service worker response in chrome developer tools.

If you choose network-first approach, you can avoid showing old content on initial load, but loose significant performance benefits that comes with caching.

Only two events…
================

In essence, there are **only two events** that will automatically trigger a PWA update:

1.  A change in the linked `manifest.json`; e.g. a changed icon file or a changed `scope` or `start_url`.
2.  A one-character change in the controlling `service-worker.js`. Hence, if you store the version number in a `const` in this file and change it, an update of the PWA will be triggered.

When a change is detected, the new version will normally be activated only with the next PWA load. So, in all, **two reloads** are necessary to see a change.

How the update eventually is handled, is ultimately determined by the `service-worker.js`. Different update strategies may be defined in terms of the size and volatility of the PWA assets. It is also possible to activate a new service immediately.

However, there is one **important caveat.** Make sure that the **browser cache expiry directive** set by the `.htaccess` file of your asset server is set to a really short duration (e.g. `hours`) or even to [**none**](https://stackoverflow.com/a/66756683/2192488). Failing to do so, will result in the browser not seeing any change for days to come in the `manifest.json` nor the `service-worker.js`.

More details about service worker behaviour are available from [Google Web Fundamentals](https://developers.google.com/web/fundamentals/primers/service-workers/lifecycle).

When and how does a pwa update itself

清除Service Worker的缓存通常涉及以下几个步骤：

1. **注销Service Worker**：
   - 打开浏览器的开发者工具。
   - 转到“Application”面板。
   - 在左侧边栏中找到“Service Workers”。
   - 点击“Unregister”以注销当前域名下的Service Worker。

2. **清除缓存**：
   - 在相同的“Application”面板中，找到“Cache Storage”。
   - 展开“Cache Storage”部分，列出所有的缓存。
   - 右键点击需要删除的缓存，选择“Delete”来清除缓存。

3. **使用代码清除缓存**：
   可以在Service Worker的脚本中编写代码来清除缓存。例如：

   ```javascript
   self.addEventListener('activate', event => {
     event.waitUntil(
       caches.keys().then(cacheNames => {
         return Promise.all(
           cacheNames.map(cacheName => {
             // 假设'v1'是你想要保留的缓存的版本
             if (cacheName !== 'v1') {
               console.log('Service Worker: 清除旧缓存', cacheName);
               return caches.delete(cacheName);
             }
           })
         );
       })
     );
   });
   ```

   上述代码会在Service Worker激活时运行，它会遍历所有的缓存，并删除那些版本不是`'v1'`的缓存。

除了这些步骤，重要的是确保在更新Service Worker脚本后，让用户的浏览器获取到最新的Service Worker文件。通常，这可以通过更改Service Worker文件的内容来实现，因为浏览器会检查文件内容是否有变化来决定是否需要安装新的Service Worker。

例如，如果我刚完成一个项目，需要更新Service Worker以及对应的缓存，我会更新Service Worker脚本，可能是修改内部的缓存策略或者版本标签，然后将修改后的脚本部署到服务器。这样用户下次访问时，浏览器会检测到Service Worker脚本的内容更新，触发安装新的Service Worker，并在activate事件中清除旧的缓存。

总的来说，清除Service Worker的缓存需要综合运用开发者工具和编写Service Worker代码的方式来实现。这对于保持应用的性能和确保用户获得最新内容非常重要。

If you know the cache name you can simply call [`caches.delete()`](https://developer.mozilla.org/en-US/docs/Web/API/CacheStorage/delete) from anywhere you like in the worker:

    caches.delete(/*name*/);
    

And if you wanted to wipe all caches (and not wait for them, say this is a background task) you only need to [add this](https://developer.mozilla.org/en-US/docs/Web/API/CacheStorage/keys):

    caches.keys().then(function(names) {
        for (let name of names)
            caches.delete(name);
    });

Use this to delete outdated caches:

    self.addEventListener('activate', function(event) {
      event.waitUntil(
        caches.keys().then(function(cacheNames) {
          return Promise.all(
            cacheNames.filter(function(cacheName) {
              // Return true if you want to remove this cache,
              // but remember that caches are shared across
              // the whole origin
            }).map(function(cacheName) {
              return caches.delete(cacheName);
            })
          );
        })
      );
    });

Typically you update the `CACHE_NAME` in your service workers JS file so your worker installs again:

    self.addEventListener('install', evt => {
      evt.waitUntil(
        caches.open(CACHE_NAME).then(cache => cache.addAll(inputs))
      )
    })
    

Alternatively, to _clear_ the cache for a PWA find the cache name:

    self.caches.keys().then(keys => { keys.forEach(key => console.log(key)) })
    

then run the following to delete it:

    self.caches.delete('my-site-cache')
    

Then refresh the page.

If you see any worker-related errors in the console after refreshing, you may also need to unregister the registered workers:

    navigator.serviceWorker.getRegistrations()
      .then(registrations => {
        registrations.forEach(registration => {
          registration.unregister()
        }) 
      })

The most elegant solution, with async/await:

    const cacheName = 'v2';
    
    self.addEventListener('activate', event => {
    // Remove old caches
      event.waitUntil(
        (async () => {
          const keys = await caches.keys();
          return keys.map(async (cache) => {
            if(cache !== cacheName) {
              console.log('Service Worker: Removing old cache: '+cache);
              return await caches.delete(cache);
            }
          })
        })()
      )
    })

This is the only code that worked for me. It is my adaptation of [Mozilla documentation](https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API/Using_Service_Workers#Deleting_old_caches) :

    //Delete all caches and keep only one
    const cachNameToKeep = 'myCache';
    
    //Deletion should only occur at the activate event
    self.addEventListener('activate', event => {
        var cacheKeeplist = [cacheName];
        event.waitUntil(
            caches.keys().then( keyList => {
                return Promise.all(keyList.map( key => {
                    if (cacheKeeplist.indexOf(key) === -1) {
                        return caches.delete(key);
                    }
                }));
            })
    .then(self.clients.claim())); //this line is important in some contexts
    });

How to clear cache of service worker?

在Cypress中，等待某个元素消失可以通过多种方式来实现。最常用的方法是利用`.should()`断言连同`not.exist`或者`not.be.visible`，来等待元素从DOM中消失或不再可见。以下是几种方法的示例：

### 使用 `should('not.exist')`

如果你希望等待一个元素从DOM中彻底消失，你可以这样做：

```javascript
cy.get('.some-element').should('not.exist');
```

这会告诉Cypress一直等待，直到页面上不再存在带有`.some-element`类的元素。

### 使用 `should('not.be.visible')`

如果元素仍然存在于DOM中，但你希望它不可见（例如，通过CSS隐藏），可以使用：

```javascript
cy.get('.some-element').should('not.be.visible');
```

这会告诉Cypress等待，直到`.some-element`不再对用户可见。

### 使用 `wait` 结合 `should`

在某些情况下，如果后端操作需要时间，并且这个操作会导致元素消失，你可能需要结合使用`wait`和`should`命令：

```javascript
cy.wait('@yourApiCall');
cy.get('.some-element').should('not.exist');
```

这个例子中，`cy.wait('@yourApiCall')`会等待一个别名为`yourApiCall`的API调用完成。完成后，Cypress会继续等待`.some-element`元素消失。

### 注意事项

- 确保你的选择器是具体且唯一的。如果选择器不唯一（例如，页面上有多个相同的元素），Cypress可能会找到其他的元素，而不是你想要它等待消失的那个。

- 如果你的应用使用动画，那么可能需要增加一个超时时长，因为元素的消失可能不是立即发生的：

  ```javascript
  cy.get('.animated-element').should('not.be.visible', { timeout: 10000 });
  ```

  这会增加Cypress等待元素不可见的超时时长至10秒。

通过这些方法，你可以告诉Cypress等待一个元素消失，这是在自动化测试中常见的一个需求，特别是在测试具有异步行为的Web应用时。

How to wait for element to disappear in cypress

当您想要卸载 Service Worker 时，可以通过几个步骤来实现：

1. **开发者工具中卸载：**

   如果是在开发过程中，可以直接通过浏览器的开发者工具来卸载 Service Worker。以下以 Google Chrome 浏览器为例：

   - 打开需要卸载 Service Worker 的网站。
   - 按 `F12` 或者右键选择“检查”打开开发者工具。
   - 切换到“Application”标签页。
   - 在左侧边栏的“Service Workers”选项下，可以看到当前激活的 Service Worker。
   - 有一个 "Unregister" 的按钮，点击它可以卸载当前的 Service Worker。

2. **编程卸载：**

   如果您希望在网站上编程实现卸载 Service Worker，可以通过以下代码实现：

   ```javascript
   if ('serviceWorker' in navigator) {
     navigator.serviceWorker.getRegistrations().then(function(registrations) {
       for (let registration of registrations) {
         registration.unregister();
       }
     }).catch(function(error) {
       console.log('Service Worker 注销失败: ', error);
     });
   }
   ```

   上面的代码段会找到所有注册的 Service Worker，并逐个注销它们。

3. **清除浏览器数据：**

   另一种卸载 Service Worker 的方法是清除网站的浏览器数据，包括缓存和本地存储。

   - 在 Chrome 浏览器中，可以按 `Ctrl+Shift+Delete` 快捷键打开“清除浏览数据”对话框。
   - 选择“高级”选项卡，勾选“Cookie 和其他站点数据”以及“缓存的图片和文件”。
   - 点击“清除数据”。

   这将删除所有的 Service Worker，以及相关的缓存和数据。

4. **手动修改Service Worker代码：**

   可以在 Service Worker 的代码中添加一个自毁逻辑，当满足特定条件时，自动卸载自身。例如：

   ```javascript
   self.addEventListener('install', (event) => {
     if (someCondition) {
       self.skipWaiting(); // 忽略等待，立即激活
     }
   });

   self.addEventListener('activate', (event) => {
     if (someCondition) {
       self.registration.unregister().then(() => {
         return self.clients.matchAll();
       }).then((clients) => {
         clients.forEach(client => client.navigate(client.url)); // 刷新页面
       });
     }
   });
   ```

   在上述代码中，`someCondition` 是一个占位符，表示某个您决定卸载 Service Worker 的条件。当条件满足时，Service Worker 将自我注销，并刷新所有的客户端页面。

通过这些方法，您可以有效地卸载 Service Worker。不过需要注意的是，卸载后相关的缓存功能将不再可用，如果是用户的设备上执行卸载操作，可能会影响到网站的离线功能和加载性能。因此，在执行卸载操作之前，请确保这是您所期望的。

### Removing Service Workers Programmatically:

You can remove service workers programmatically like this:

    navigator.serviceWorker.getRegistrations().then(registrations => {
        for (const registration of registrations) {
            registration.unregister();
        } 
    });
    

Docs: [getRegistrations](https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerContainer/getRegistrations), [unregister](https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration/unregister)

### Removing Service Workers Through The User Interface

You can also remove service workers under the Application tab in Chrome Devtools.

You can also go to the URL: **chrome://serviceworker-internals/** and unregister a serviceworker from there.

You can do this through **Chrome Developer Tool** as well as **Programatically**.

1.  Find all running instance or service worker by typing
    
    > **chrome://serviceworker-internals/**
    
    in a new tab and then select the serviceworker you want to unregister.
    
2.  Open Developer Tools (F12) and Select Application. Then Either
    
    > **Select Clear Storage -> Unregister service worker**
    
    or
    
    > **Select Service Workers -> Choose Update on Reload**
    
3.  Programatically
    

    if(window.navigator && navigator.serviceWorker) {
      navigator.serviceWorker.getRegistrations()
      .then(function(registrations) {
        for(let registration of registrations) {
          registration.unregister();
        }
      });
    }

Run code snippetHide results

Expand snippet

In Google Chrome, you can go to **Developer tools (F12) -> Application -> Service worker** and **unregister** the service workers from the list for that specific domain.

[![Screenshot](https://i.stack.imgur.com/RtV2C.png)](https://i.stack.imgur.com/RtV2C.png)

This method is effective in development mode of a site and mostly they run on `localhost` which is you may need for other project's development.

FYI, in case you are using MacOS **Safari** browser, there is one way to forcibly unregister a service worker (steps and images for Safari 12.1):

1.  Safari > Preferences... > Privacy > Manage Website Data… [![Safari Preferences : Privacy](https://i.stack.imgur.com/yiEbw.png)](https://i.stack.imgur.com/yiEbw.png)
    
2.  Enter domain name (ex. 'localhost'), click "Remove" [![Safari Preferences : Privacy : manage website data](https://i.stack.imgur.com/am2s2.png)](https://i.stack.imgur.com/am2s2.png)
    

**Note:** In addition to service workers, this also will erase all caches, cookies, and databases for this domain.

How do i uninstall a service worker

在Cypress中等待某个元素消失，我们通常会用到`.should('not.exist')`断言。这将会让Cypress重试断言直到它通过为止，即直到元素不再存在于DOM中。这是一个非常实用的特性，尤其是当进行异步操作，例如等待一个加载指示器消失之后再进行下一步操作。

例如，假设您有一个加载指示器，它在异步操作期间在页面上显示，操作完成后消失。加载指示器的HTML元素可能是这样的：

```html
<div id="loading-indicator">Loading...</div>
```

当您想要在测试中等待这个加载指示器消失时，可以这样编写Cypress代码：

```javascript
// 等待加载指示器消失
cy.get('#loading-indicator').should('not.exist');
```

这段代码会获取ID为`loading-indicator`的元素，并断言它应该不存在。Cypress会不断尝试这个断言，直到默认的超时时间（通常是4秒，但是可以通过配置进行修改）结束，如果在这段时间内元素消失了，测试就会继续进行。如果元素没有在超时时间内消失，测试将会失败。

此外，如果需要等待某个元素不可见（即它仍然存在于DOM中，但是不再是可见状态），可以使用`.should('not.be.visible')`断言。

例如，如果加载指示器变成了不可见状态，但没有从DOM中移除，可以这样做：

```javascript
// 等待加载指示器不可见
cy.get('#loading-indicator').should('not.be.visible');
```

这两种方法允许你在Cypress测试中处理元素消失的情况，确保在断言和操作之间有适当的同步。

IMHO the cleanest way is not to use waits nor timeouts with get, this is kinda an antipattern.

I would recommend to use [Cypress waitUntil](https://www.npmjs.com/package/cypress-wait-until) command and use something like:

     cy.waitUntil(function() {
      return cy.get('element').should('not.exist');
     })
    

or depending on the app code you can use `not.be.visible`.

`cypress-wait-until` did not work for me. I just used the basic:

    cy.get('.ant-drawer-body').should('not.exist');
    

It waits automatically.

If you specifically need to wait, you could use the [`wait()`](https://docs.cypress.io/api/commands/wait.html) function of cypress before making an assertion, and provide the amount of time to wait before timeout.

But note, this is an anti-pattern as you can find in the docs:

> You almost never need to wait for an arbitrary period of time. There are always better ways to express this in Cypress.

That said, if your loading indicator is bound to some network request, you can wait for them to finish before making an assertion. This could be achieved with something like [this](https://docs.cypress.io/api/commands/wait.html#Alias) example:

    // Wait for the route aliased as 'getAccount' to respond
    // without changing or stubbing its response
    cy.server()
    cy.route('/accounts/*').as('getAccount')
    cy.visit('/accounts/123')
    cy.wait('@getAccount').then((xhr) => {
      // we can now access the low level xhr
      // that contains the request body,
      // response body, status, etc
    })
    

More info about waiting for requests could be found [here](https://docs.cypress.io/guides/guides/network-requests.html#Waiting).

Also, make sure that you really want to use `.should('not.exist')` and not `.should('not.be.visible')`.

Loading spinner implementations often just hide the element rather than removing it from the DOM. Hence, `should("not.exist")` won't work for them.

`cy.get("element").should("not.be.visible")` is the right approach in such cases (as [Diogo's answer](https://stackoverflow.com/questions/53672387/how-to-wait-for-element-to-disappear-in-cypress#answer-53673043) already hinted).

`.findByTestId('loading-spinner-data-testid').should('not.be.visible')`

This works in a similar context for me.

As of `"@testing-library/cypress": "^5.3.1",`

Just make sure you give your spinner component a data-testid attribute.

`<LoadingSpinner data-testid='loading-spinner-data-testid'>`

How to wait for element to disappear in cypress?

在 Cypress 中，可以通过多种方式访问 `baseURL` 的值。`baseURL` 是在 Cypress 的配置文件中指定的，通常用来表示应用的根地址，这样就可以在测试中仅仅使用相对路径。以下是访问 `baseURL` 的几种方法：

1. **通过 `cy.visit()` 使用相对路径**:
   当您在 `cy.visit()` 使用相对路径时，Cypress 会自动将 `baseURL` 作为前缀添加到路径中。例如，如果您设置了 `baseURL` 为 `https://example.com`，您可以这样使用：

   ```javascript
   cy.visit('/page'); // 实际访问的 URL 将是 https://example.com/page
   ```

2. **通过 Cypress 配置命令**:
   您可以使用 `Cypress.config()` 函数访问当前的配置，包括 `baseURL`。例如：

   ```javascript
   const baseURL = Cypress.config('baseUrl');
   console.log(baseURL); // 输出配置文件中设置的 baseURL
   ```

3. **在测试中动态设置**:
   如果你需要在测试执行过程中动态地更改 `baseURL`，你也可以使用 `Cypress.config()` 方法：

   ```javascript
   Cypress.config('baseUrl', 'https://newexample.com');
   // 之后的 cy.visit('/') 会访问 https://newexample.com/
   ```

4. **环境变量**:
   还可以通过设置环境变量的方式来覆盖配置文件中的 `baseURL`。在命令行中运行 Cypress 时，使用 `CYPRESS_BASE_URL` 环境变量：

   ```shell
   CYPRESS_BASE_URL=https://anotherexample.com npx cypress open
   ```

   在测试中，`baseURL` 会被设置为 `https://anotherexample.com`。

作为一个实际的例子，假设我们在测试中需要访问一个登录页面，而这个页面的路径是 `/login`。我们的 `baseURL` 配置为 `https://example.com`，我们可以编写以下的 Cypress 测试代码：

```javascript
describe('Login Page Test', () => {
  it('should visit the login page', () => {
    // 直接使用相对路径，Cypress 会自动使用 baseURL
    cy.visit('/login');
    
    // 做一些登录页面的断言...
  });
  
  it('should dynamically get the baseURL and construct the full URL', () => {
    // 获取 baseURL
    const baseURL = Cypress.config('baseUrl');
    
    // 使用获取的 baseURL 构造完整的 URL 并访问
    cy.visit(`${baseURL}/login`);
    
    // 做一些登录页面的断言...
  });
});
```

在第一个测试用例中，我直接使用 `cy.visit('/login')`，Cypress 自动加上了 `baseURL`。在第二个测试用例中，我首先获取 `baseURL` 的值，然后手动构造了完整的 URL 来访问登录页面。这两种方式都可以根据测试的需要选择使用。

You can use the [`Cypress.config()`](https://docs.cypress.io/api/cypress-api/config#Syntax) command.

To get `baseUrl` value use `Cypress.config().baseUrl` or `Cypress.config('baseUrl')`.

`cy.visit('/')` will visit the baseUrl if you have it defined in your Cypress e2e config. ([Source](https://docs.cypress.io/api/commands/visit#Syntax))

How to access the value of baseURL in Cypress

在Cypress中，要在所有测试运行之前执行一些公共代码，我们通常使用`before`或`beforeEach`钩子。`before`钩子在测试文件中的所有测试运行之前执行一次，而`beforeEach`钩子则在每个测试用例运行之前都会执行。

这里有个示例：

如果您想在所有测试前只执行一次某些代码，您可以在测试文件的顶层使用`before`钩子：

```javascript
// 在所有测试前只执行一次
before(() => {
  // 这里可以放置你的公共代码，比如：
  // 登录操作
  cy.login('username', 'password'); // 假设你有一个封装好的登录命令
  // 设置测试数据或者环境
  cy.setupTestData();
});
```

如果需要在每个测试用例之前执行代码，可以使用`beforeEach`钩子：

```javascript
// 在每个测试用例之前都执行
beforeEach(() => {
  // 这里可以放置你的公共代码，比如：
  // 每次都要确保从登陆页面开始
  cy.visit('/login'); // 访问登录页面
  // 你可能需要清除浏览器的localStorage或cookies
  cy.clearLocalStorage();
  cy.clearCookies();
  // 每个测试用例都需要的初始化操作
  cy.initializeTestContext();
});
```

这些钩子应该放在你的测试文件顶部，通常在描述测试套件的`describe`块外面或里面。将它们放在`describe`块外面意味着它们会在该文件中定义的所有`describe`块之前运行。放在`describe`块内部，则只会影响该`describe`块中的测试用例。

另外，如果你有多个测试文件，并且希望有一些代码在这些测试文件中的每个文件执行前都运行一次，你可以使用Cypress的`support`文件夹中的`index.js`文件。在那里放置的代码会在每个测试文件执行前运行。

例如，在`cypress/support/index.js`文件中：

```javascript
// 这将在每个测试文件之前执行一次
before(() => {
  // 公共初始化代码，比如设置API服务器的状态
  cy.initializeApiServer();
});

// 这将在每个测试文件的每个测试用例之前执行
beforeEach(() => {
  // 通用的每个测试用例前的逻辑，比如登录
  cy.loginToApplication();
});
```

记得在使用这些钩子时要注意它们的作用域和执行顺序，以确保测试环境的正确设置。

**Short answer:** You can write your login command in a `before` hook within the `supportFile` ([the file that is loaded automatically before your other spec files](https://on.cypress.io/configuration#Folders-Files)). This `before` hook will run before any of the code in your other test files.

* * *

**Recommendations:** That being said, this approach leaves little flexibility for variation in your individual test files that you may want in the future like:

*   What if you want to seed the database differently for one test?
*   What if you want to log in as a different user with different permissions?
*   What if you need to do something in `onBeforeLoad` once?

I would recommend just having the login command in a `before` hook in each individual spec file.

I would also _further_ recommend having your login command in a `beforeEach` hook to [avoid sharing _any_ state in between tests](https://docs.cypress.io/guides/references/best-practices.html#Having-tests-rely-on-the-state-of-previous-tests).

Now in **Cypress v12** the appropriate way to do this is with the [Before Run API](https://docs.cypress.io/api/plugins/before-run-api).

**cypress.config.js**

    const { defineConfig } = require('cypress')
    
    module.exports = defineConfig({
      // setupNodeEvents can be defined in either
      // the e2e or component configuration
      e2e: {
        setupNodeEvents(on, config) {
          on('before:run', (details) => {
            /* code that needs to run before all specs */
          })
        },
        experimentalInteractiveRunEvents: true,   // use for cypress open mode
      },
    })

describe('Hooks', function() {
        before(function() {
            // runs once before all tests in the block
        })
    })
    

[https://docs.cypress.io/guides/core-concepts/writing-and-organizing-tests.html#Hooks](https://docs.cypress.io/guides/core-concepts/writing-and-organizing-tests.html#Hooks)

I would login before EACH test because there could be things that happen in a previous test that affects the results of the current test. With a fresh login, you're starting with a clean state every time. If you want to test a "chain" of unrelated actions (action A THEN action B), then write that as a separate test, but have basic functionality in individual tests.

    describe('/page'), () => {
      beforeEach(() => {
        cy.login()        // custom command that handles login w/o UI
        cy.visit('/page') // go to the page you are testing
      })
    
      // tests
    })
    

You should include a beforeEach block in every test file. This block should login and navigate to the page in question.

`cypress/support/e2e.ts`

    before(() => {
      // do stuff
    })
    

Use `before` to run 1-time before every test or use `beforeEach`. to run before each individual test.

How can I execute code before all tests suite with Cypress?

在 Koa 中实现文件下载功能通常涉及以下几个步骤：

1. **处理请求**：首先，你需要定义一个路由和对应的处理函数来处理下载请求。
2. **文件定位**：处理函数中需要定位到要下载的文件在服务器上的路径。
3. **设置响应头**：为了通知浏览器这是一个文件下载响应，需要设置适当的 `Content-Disposition` 和 `Content-Type` 响应头。
4. **发送文件**：最后，使用 Koa 的响应对象来发送文件内容回客户端。

以下是一个简单的例子，演示了如何在 Koa 应用程序中实现文件下载功能：

```js
const Koa = require('koa');
const send = require('koa-send');
const path = require('path');
const app = new Koa();

// 定义一个路由用于处理下载请求
app.use(async (ctx) => {
    // 假设我们要下载的文件名是固定的
    const fileName = 'example.txt';

    // 设置文件的完整路径
    const filePath = path.join(__dirname, 'public', fileName);

    // 设置响应头
    ctx.set('Content-Disposition', `attachment; filename=${fileName}`);
    ctx.set('Content-Type', 'application/octet-stream');

    // 发送文件内容作为响应
    await send(ctx, filePath, { root: __dirname });
});

app.listen(3000, () => {
    console.log('Server running on http://localhost:3000');
});
```

在这个例子中，当客户端向服务器发送请求时，Koa 应用程序会通过 `koa-send` 模块来发送位于 `public` 目录下的 `example.txt` 文件。`Content-Disposition` 响应头被设置为 `attachment`，以及文件的名称，这样浏览器就知道它应该提示用户保存文件而不是直接在浏览器中显示文件的内容。`Content-Type` 被设置为 `application/octet-stream`，这是一个通用的二进制文件类型，告诉浏览器这是一个二进制文件。

请注意，这个例子中的文件名是硬编码的，但在实践中，你可能需要根据请求动态地确定文件名和路径。此外，你还可能需要处理诸如文件不存在、权限不足等潜在错误情况。

For anyone else who sees this in the future, it's worth mentioning that there is a built in `attachment` method on the `response` object that you can use to set the `Content-Disposition` to `attachment` with a specified filename. So you can do this:

    this.attachment('hello.txt')
    

And it would be the same thing as the following:

    this.set('Content-disposition', 'attachment; filename=hello.txt')
    

* * *

For Koa 2:

    ctx.attachment('hello.txt')

You should be able to simple set `this.body` to the file stream

    this.body = fs.createReadStream(__dirname + '/test.zip');
    

then set the response headers as appropriate.

    this.set('Content-disposition', 'attachment; filename=' + filename);
    this.set('Content-type', mimetype);

Browser default behaviour is to display the file, not to download it. To enforce download you need to do this:

    this.header("Content-Type", "application/force-download")
    this.header('Content-disposition', 'attachment; filename=' + filename);

Bit of a different file download example with error checking, using Node with Koa 2. I am not sure if it is necessary to destroy the stream afterwards as described here [https://github.com/jshttp/content-disposition#options](https://github.com/jshttp/content-disposition#options)

    router.get('/downloads/:version/:file', async function(ctx) {
      const fileName = `${__dirname}/downloads/${ctx.params.version}/${ctx.params.file}`;
      try {
        if (fs.existsSync(fileName)) {
          ctx.body = fs.createReadStream(fileName);
          ctx.attachment(fileName);
        } else {
          ctx.throw(400, "Requested file not found on server");
        }
      } catch(error) {
        ctx.throw(500, error);
      }  
    });
    

In browser sample: [https://myserver.com/downloads/1.0.0/CoolAppFile.zip](https://myserver.com/downloads/1.0.0/CoolAppFile.zip)

How to achieves file download with koa?

`koa-body`和`koa-bodyparser`都是针对Koa框架的中间件，用于处理HTTP请求体（body），但它们之间有一些关键的区别：

### koa-bodyparser
- **限制性**：`koa-bodyparser`较为简单，主要用于解析JSON和表单提交的数据。
- **功能**：它将解析好的body放置于`ctx.request.body`中。
- **文件上传**：`koa-bodyparser`不支持文件上传功能；它不能处理`multipart/form-data`类型的请求体，这意味着它不适用于文件上传的场景。
- **定制性**：它的定制性较弱，主要针对常见的`content-type`进行解析。

### koa-body
- **功能性**：`koa-body`是一个更全面的解决方案，它不仅支持JSON和表单数据的解析，还支持文件上传。
- **文件上传**：它可以处理`multipart/form-data`类型的请求体，因此可以用于文件上传；在处理文件上传时，`koa-body`会将上传的文件放置在`ctx.request.files`中。
- **定制性**：`koa-body`提供了更多的定制选项，如文件大小限制、文件类型限制等，给予开发者较大的灵活性。
- **依赖**：`koa-body`可能会有更多外部依赖，因为它需要处理更多类型的数据，包括文件的临时存储。

### 使用场景举例

**koa-bodyparser使用场景：**
如果您正在构建一个API服务，该服务只接受JSON格式的数据或简单的表单数据，使用`koa-bodyparser`就足够了。例如，您有一个用户登录的端点，它接受一个用户名和密码作为表单提交，这种情况下`koa-bodyparser`是合适的。

```javascript
const Koa = require('koa');
const bodyParser = require('koa-bodyparser');

const app = new Koa();

app.use(bodyParser());

app.use(async ctx => {
  const { username, password } = ctx.request.body;
  // 处理登录逻辑
  ctx.body = '登录成功';
});

app.listen(3000);
```

**koa-body使用场景：**
如果您的应用需要更复杂的数据处理，如文件上传（例如用户头像上传），则需要使用`koa-body`。

```javascript
const Koa = require('koa');
const koaBody = require('koa-body');

const app = new Koa();

app.use(koaBody({ multipart: true }));

app.use(async ctx => {
  const { files, fields } = ctx.request;
  // files 有上传的文件
  // fields 有其他表单字段
  // 处理上传逻辑
  ctx.body = '文件上传成功';
});

app.listen(3000);
```

综上所述，选择哪个中间件取决于您的应用场景。如果您只需要处理JSON或URL编码的表单数据，`koa-bodyparser`可能更简单且更适合。如果您需要处理包括文件上传在内的更复杂数据类型，那么`koa-body`会是更好的选择。

### \[New answer\]

`koa-body` now support koa version 2. The main difference now remains about file payload parsing. The `koa-bodyparser` cannot parse files, i.e. `multipart/form-data`.

### \[Old answer\]

Oh, I got it.

[https://github.com/koajs/koa/wiki](https://github.com/koajs/koa/wiki)

koa-body supports koa v1, koa-bodyparser supports koa v2.

And former can parse file, but later can't.

Thanks.

Both are Koa body parser middleware. I recently faced an issue where I wanted to handle file upload and there comes the main difference.

Koa-body supports -- koa, urlencoded, multipart, json, body, parser, form and

koa-bodyparser supports -- json, urlencoded, koa, body.

So if you are looking for file uploading features , go ahead with koa-body or koa-better-body (which has more wider scopes)

[Here is detailed reference](https://npmcompare.com/compare/koa-better-body,koa-body,koa-bodyparser)

Whats the difference between koa body vs koa bodyparser

在 Koa.js 中为所有响应添加自定义 header，通常可以通过中间件的方式实现。在 Koa 中，中间件是处理 HTTP 请求和响应的函数，它们按照添加的顺序被执行。为了给所有响应加上自定义 header，我们可以创建一个中间件，并将其放在其他所有中间件之前。

下面是一个如何实现这一功能的示例：

```javascript
const Koa = require('koa');
const app = new Koa();

// 自定义 header 的中间件
app.use(async (ctx, next) => {
    // 在这里设置自定义 header
    ctx.set('X-Custom-Header', 'YourCustomHeaderValue');

    // 调用下一个中间件
    await next();

    // 如果你还需要在响应后执行一些操作，可以在此处添加代码
});

// 其他中间件
// ...

// 一个简单的响应示例
app.use(async ctx => {
    ctx.body = 'Hello World';
});

app.listen(3000);
```

上面的代码中，我们定义了一个中间件，它通过 `ctx.set` 方法设置了自定义的 header `X-Custom-Header`。在调用 `await next()` 之后，当前中间件会暂停执行，直到下游的中间件处理完毕后才可能继续执行（如果有需要在响应后执行的操作）。

在上面的例子中，如果你想要为所有响应设置多个自定义 header，你可以重复使用 `ctx.set` 方法，如下所示：

```javascript
app.use(async (ctx, next) => {
    ctx.set('X-Custom-Header-One', 'ValueOne');
    ctx.set('X-Custom-Header-Two', 'ValueTwo');
    // ...设置更多的 header

    await next();
});
```

还有一点需要注意的是，如果你想要覆盖 Koa 默认的某些 header，比如 `Content-Type` 或 `Content-Length`，你可能需要在响应体被设置之后再覆盖它们，因为 Koa 会基于响应体来自动设置这些 header。

确保自定义的 header 不与 HTTP 规范中的标准 header 冲突，并且符合你的应用程序的安全策略。

下面的代码可以实现何对所有的请求响应设置Header   

```
app.use(async (ctx, next) => {
  ctx.set('Access-Control-Allow-Origin', '*');
  ctx.set('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
  ctx.set('Access-Control-Allow-Methods', 'POST, GET, PUT, DELETE, OPTIONS');
  await next();
});
```

How do i set headers to all responses in koa js?

在 Koa.js 中，可以通过请求对象（`ctx.request`）访问客户端的 IP 地址。最直接的方法是使用 `ctx.request.ip` 属性。但在实际部署中，很多应用会放在代理（如 Nginx）后面，这时直接获取的 IP 可能是代理服务器的 IP。为了获取实际的客户端 IP，通常会通过 `X-Forwarded-For` 请求头来获取。

这里有一个简单的例子说明如何在 Koa.js 中获取客户端的真实 IP 地址：

```javascript
const Koa = require('koa');
const app = new Koa();

// Trust proxy headers
app.proxy = true;

app.use(async ctx => {
  // 获取真实客户端 IP 地址
  const clientIp = ctx.request.ip;

  // 如果使用了代理，那么可以通过以下方式获取真实 IP
  // const xForwardedFor = ctx.request.header['x-forwarded-for'];
  // const realClientIp = xForwardedFor ? xForwardedFor.split(',')[0] : clientIp;

  ctx.body = `Your IP address is: ${clientIp}`;
});

app.listen(3000, () => {
  console.log('Server is running on http://localhost:3000');
});
```

在上面的代码中：

- `app.proxy = true;` 告诉 Koa 信任代理头信息（比如 `X-Forwarded-For`），这通常在应用部署在代理之后时设置。
- `ctx.request.ip` 用于获取请求的 IP 地址。若设置了 `app.proxy = true;`，Koa 会自动考虑 `X-Forwarded-For` 头信息。
- 我们注释掉的两行代码显示了如何手动从 `X-Forwarded-For` 头信息中提取客户端的真实 IP。这可能在不同的部署设置中有所不同，因为有些代理会添加多个 IP 地址到 `X-Forwarded-For`。

确保在生产环境中谨慎设置 `app.proxy = true;`，因为它会信任请求头中的 IP 地址。只有当您确信代理是可信的并且已正确配置时，才应该这样做。错误地信任代理头信息可能会导致安全问题。

**Koa 1:**

Assuming you have no reverse proxy in place, you can use `this.request.ip` like this:

    router.get('/admin.html', function *(next) {
        const clientIP = this.request.ip;
        this.body = `Hello World ${clientIP}`;
    });
    

This feature is documented in the [request](https://github.com/koajs/koa/blob/master/docs/api/request.md) documentation. You can always access said `request` object as `this.request`.

If you have a reverse proxy in place, you'll always get the IP address of the reverse proxy. In this case, it's more tricky: In the reverse proxy configuration, you need to add a special header, e.g. `X-Orig-IP` with the original client IP.

Then, you can access it in koa with:

    const clientIp = this.request.headers["X-Orig-IP"];
    

**Koa 2:**

The approach is quite similar, only the syntax is slightly different:

    router.get('/', async (ctx, next) => {
        const clientIP = ctx.request.ip;
        ctx.body = `Hello World ${clientIP}`;
    })

If you add `app.proxy=true` you can still use `request.ip` without having to worry about the IP headers.

I had the same problem but resolved it by using this module found on NPM `request-ip`

in koa it can be simply used `userIp = requestIp.getClientIp(ctx.request)`

The user ip is determined by the following order:

    X-Client-IP
    X-Forwarded-For (Header may return multiple IP addresses in the format: "client IP, proxy 1 IP, proxy 2 IP", so we take the the first one.)
    CF-Connecting-IP (Cloudflare)
    Fastly-Client-Ip (Fastly CDN and Firebase hosting header when forwared to a cloud function)
    True-Client-Ip (Akamai and Cloudflare)
    X-Real-IP (Nginx proxy/FastCGI)
    X-Cluster-Client-IP (Rackspace LB, Riverbed Stingray)
    X-Forwarded, Forwarded-For and Forwarded (Variations of #2)
    req.connection.remoteAddress
    req.socket.remoteAddress
    req.connection.socket.remoteAddress
    req.info.remoteAddress
    

If an IP address cannot be found, it will return null.

所有问题