Computed Properties vs Watchers in Vue.js

Computed Properties

Computed properties are used to calculate the value of a property based on some other conditions. They are declared using the computed keyword, and the value of the computed property is a function that returns a value.

Computed properties have the following advantages:

They are cached, so they only recalculate when the value of their dependencies changes. This can improve performance, especially if the computed property is expensive to calculate.
They are reactive, so they will automatically update when the value of their dependencies changes. This makes them ideal for displaying data that is derived from other data.

Here is an example of a computed property:

computed: {
    totalItems() {
        return this.items.length;
    }
},

Watchers

Watchers are used to watch for changes in a property and perform an action when the change occurs. They are declared using the watch keyword, and the value of the watcher is a function that is called when the property changes.

Watchers have the following advantages:

They can be used to perform asynchronous or expensive operations when the value of a property changes.
They can be used to debounce or throttle the execution of an action, which can improve performance.

Here is an example of a watcher:

watch: {
    input (val) {
        this.message = `The input value is now ${val}`;
    }
},

Conclusion

Computed properties and watchers are both powerful tools that can be used to manipulate data in Vue.js. However, they have different purposes and should be used in different situations. Computed properties are best used for calculating values that are derived from other data, while watchers are best used for performing actions when the value of a property changes.

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