What is the benefit of using watchEffect over watch in Vuejs ?

In Vue.js, both watchEffect and watch are functions used to track changes in one or more sources reactively and execute side effects. However, they differ in usage and application scenarios. Below, I will detail some advantages of using watchEffect over watch.

Automatic Tracking of Dependencies

watchEffect automatically tracks all reactive references and component states used within it by default. This means users do not need to explicitly declare dependencies; watchEffect automatically collects and listens to all relevant dependencies. This automatic tracking of dependencies makes the code more concise and maintainable.

For example, if you have a component containing multiple reactive data, as follows:

javascript
export default {
  setup() {
    const firstName = ref('John');
    const lastName = ref('Doe');

    watchEffect(() => {
      console.log(`Full name is ${firstName.value} ${lastName.value}.`);
    });

    return { firstName, lastName };
  }
}

In this example, watchEffect automatically tracks changes to firstName and lastName without manual specification.

Simplifying Reactive Logic

watchEffect emphasizes the overall nature and automatic tracking of side effects, making the code more intuitive and concise when handling complex reactive logic. Using watchEffect reduces code volume because you do not need to explicitly list all dependencies.

Immediate Execution

watchEffect executes immediately upon initialization to set or synchronize state. In contrast, watch does not execute by default unless specified with immediate: true.

Use Cases

watchEffect is ideal for scenarios where you need to execute operations upon state changes that depend on multiple sources. It simplifies dependency management by automatically listening to all used reactive states.

To summarize, watchEffect provides a higher level of abstraction suitable for scenarios requiring automatic management of multiple dependencies, making the code more concise and understandable. For complex scenarios requiring precise control over dependencies and reaction timing, watch may be preferred.