watchers are respond to properties changes and computed also respond to properties then wh y we cannot use computed instead of watchers

watachers and computed both are same 

computerd for synchronouse and lesss logic

and watchers for async and sync and complex logic 

In Vue.js, watchers are a feature that allows you to react to changes in data properties and perform specific actions or computations when those changes occur. Watchers are commonly used when you need to perform asynchronous or computationally expensive operations based on data changes. Here's an overview of how watchers work in Vue.js:

To define a watcher, you need to use the watch option within a Vue component. The watch option accepts an object where the keys represent the data properties you want to watch, and the values are the corresponding watcher functions. s

export default {
  data() {
    return {
      message: '',
    };
  },
  watch: {
    message(newValue, oldValue) {
      // Perform actions based on the data change
      console.log('New message:', newValue);
      console.log('Old message:', oldValue);
    },
  },
};

n the example above, a watcher is defined for the message data property. Whenever message changes, the watcher function is triggered. It receives two arguments: newValue and oldValue, representing the new and old values of the property.

You can also use deep watchers to watch nested properties or an entire object. To do this, you can use the deep option set to true:

export default {
  data() {
    return {
      user: {
        name: '',
        age: 0,
      },
    };
  },
  watch: {
    user: {
      deep: true,
      handler(newValue, oldValue) {
        // Perform actions based on the data change
        console.log('New user:', newValue);
        console.log('Old user:', oldValue);
      },
    },
  },
};

In this example, any changes to the properties within the user object will trigger the watcher.

Watchers can also be used in combination with computed properties to perform more complex operations based on data changes:

export default {
  data() {
    return {
      firstName: '',
      lastName: '',
    };
  },
  computed: {
    fullName() {
      return `${this.firstName} ${this.lastName}`;
    },
  },
  watch: {
    fullName(newValue, oldValue) {
      console.log('New full name:', newValue);
      console.log('Old full name:', oldValue);
    },
  },
};

In this case, changes to the firstName or lastName properties will trigger the watcher on the computed property fullName.

Watchers are powerful for reacting to data changes and performing actions accordingly. However, it's important to use them judiciously and consider the performance implications, especially when dealing with computationally expensive operations or watching deeply nested data structures.

watchers are respond to properties changes and computed also respond to properties then wh y we cannot use computed instead of watchers

While computed properties and watchers can both respond to changes in data properties, they serve different purposes and have distinct functionalities. Here's a breakdown of the differences between computed properties and watchers in Vue.js:

Computed Properties:

1. Computed properties are derived data properties that are calculated based on the values of other data properties. They are essentially functions that are cached and only re-evaluated when their dependent properties change.
2. Computed properties are meant to provide a convenient way to compute and cache values that depend on reactive data.
3. Computed properties are used within templates and accessed as regular properties. They automatically update when their dependencies change, and the Vue reactivity system takes care of efficiently updating them.
4. Computed properties are best suited for performing synchronous and lightweight operations.
5. Computed properties are not ideal for performing asynchronous or side-effect-driven tasks.

Watchers:

1. Watchers, on the other hand, allow you to perform more complex logic when a specific data property changes. They are defined as functions that are executed whenever a watched property changes.
2. Watchers are useful when you need to perform asynchronous operations, make API calls, or perform side effects based on the change of a property.
3. Watchers provide more flexibility and control over how you respond to changes. They can execute any custom logic and perform operations based on the new and old values of the watched property.
4. Watchers are particularly helpful when you need to track changes in deeply nested properties or perform operations that cannot be achieved with computed properties alone.

In summary, while both computed properties and watchers can respond to property changes, computed properties are primarily used for synchronous and lightweight computations, while watchers are more suitable for performing complex logic, asynchronous operations, and side-effect-driven tasks. It's important to choose the appropriate approach based on the specific requirements of your application.