VueJS - Vue 3 Composition API: Computed and Watch
Using Computed Properties and Watch with Composition API
The Composition API in Vue 3 provides powerful reactivity capabilities through computed properties and watchers. This guide explores how to use these features effectively in your Vue 3 applications.
Key Points:
- Computed properties are used to create reactive derived state based on other reactive state.
- Watchers are used to perform side effects in response to reactive state changes.
- Both computed properties and watchers are essential tools for managing reactivity in Vue 3.
Computed Properties
Computed properties in the Composition API are created using the computed function. They automatically update when their dependencies change, making them ideal for derived state.
// MyComponent.vue
Count: {{ count }}
Double Count: {{ doubleCount }}
Watchers
Watchers in the Composition API are created using the watch function. They allow you to perform side effects in response to changes in reactive state.
// MyComponent.vue
Message: {{ message }}
Deep Watching
To watch deep changes in an object or array, you can set the deep option to true:
// MyComponent.vue
User: {{ user.name }}
Immediate Watching
To run a watcher immediately upon creation, set the immediate option to true:
// MyComponent.vue
Count: {{ count }}
watchEffect
The watchEffect function automatically tracks and reacts to reactive dependencies within its scope. It is useful for creating side effects that should run immediately and re-run whenever dependencies change.
// MyComponent.vue
Count: {{ count }}
Best Practices
Follow these best practices when using computed properties and watchers with the Composition API:
- Use Computed Properties for Derived State: Use computed properties to create derived state that automatically updates when dependencies change.
- Avoid Complex Logic in Watchers: Keep the logic in watchers simple to avoid performance issues and maintain readability.
- Leverage watchEffect for Immediate Reactions: Use
watchEffectfor side effects that should run immediately and re-run whenever dependencies change. - Test Thoroughly: Test your computed properties and watchers thoroughly to ensure they behave as expected in different scenarios.
Summary
This guide provided an overview of using computed properties and watchers with the Vue 3 Composition API. By leveraging these features, you can create more reactive and dynamic applications with Vue 3.