How to check whether a script is running under Node. Js ?

When running a script in the Node.js environment, it is often necessary to verify whether the script is executing in the Node.js environment or in another environment (such as a browser). This requirement is particularly important when developing modules compatible with multiple runtime environments.

To check if a script is running in the Node.js environment, you can use the following methods:

1. Check the process object

The Node.js environment provides a global object process that contains information about the current Node.js process. In browser environments, the process object is typically not available.

javascript
if (typeof process !== 'undefined' && process.versions && process.versions.node) {
    console.log('Running in the Node.js environment');
} else {
    console.log('Not running in the Node.js environment');
}

This code first checks if the process object exists, then verifies if it has a versions property and if that property contains a node field. This approach is relatively safe, preventing references to undefined variables in non-Node.js environments.

2. Use global object characteristics

In Node.js, the global object is a reference to the global object, similar to the window object in browsers. You can check for the presence of Node.js-specific global variables within the global object.

javascript
if (typeof global !== 'undefined' && global.Buffer) {
    console.log('Running in the Node.js environment');
} else {
    console.log('Not running in the Node.js environment');
}

Here, it checks for the presence of the Buffer class within the global object. Buffer is a class in Node.js used for handling binary data, which is typically not available in browser environments.

Application Example

Suppose we are developing a module that can be used in both Node.js and browser environments. We may need to choose different implementation strategies based on the runtime environment:

javascript
function fetchData() {
    if (typeof process !== 'undefined' && process.versions && process.versions.node) {
        // Node.js environment
        const fs = require('fs');
        return fs.readFileSync('/path/to/data.json', 'utf8');
    } else {
        // Browser environment
        return fetch('/data.json').then(response => response.json());
    }
}

This function fetchData uses different methods to retrieve data based on the runtime environment: in Node.js, it reads data from the file system; in the browser, it uses the fetch API to retrieve data from the network.

In summary, confirming whether a script is running under the Node.js environment typically relies on checking environment-specific objects, ensuring that the code executes correctly in the appropriate environment.