The watchEffect function in Vue3: Let you play with Vue3 responsiveness in 10 minutes

The watchEffect function in Vue3: Let you play with Vue3 responsiveness in 10 minutes

Vue3 is a recently released Vue.js framework. It is widely considered to be the latest evolution of the Vue.js framework, providing It has some new features and optimizations, the most forward-looking of which is its powerful responsive system.

Vue3’s responsive system has been improved in many aspects, one of the important improvements is the introduction of the watchEffect function. The watchEffect function is one of the cores of Vue3, which allows you to use responsive data and processing more conveniently. In this article, we will introduce the basic usage of the watchEffect function and how to use it to enhance the functionality of Vue3.

What is the watchEffect function?

The watchEffect function is a reactive system based on dependency tracking in Vue3, rather than the declarative watch function in traditional Vue.js. The watchEffect function can automatically track dependent data and automatically call the callback function when the dependent data changes.

The watchEffect function is characterized by: when the data changes, the UI will be updated immediately; when the dependent data changes, the previous callback can be automatically cleaned up and the dependent data will be logged out. This means we can create and clean up reactive functionality once we need it, rather than adding unnecessary code because we need to clean up previous callbacks.

How to use watchEffect function?

Using the watchEffect function in Vue3 is very simple, just call it in the setup function. Here is a simple example to give us a better understanding of how to use it:

<template>
  <div>
    <h1 id="count">{{count}}</h1>
    <button @click="increment">increment</button>
  </div>
</template>

<script>
import { reactive, watchEffect } from 'vue';

export default {
  setup() {
    const state = reactive({
      count: 0,
    });

    watchEffect(() => {
      console.log(`count changed to ${state.count}`);
    });

    const increment = () => {
      state.count++;
    };

    return {
      ...state,
      increment,
    };
  },
};
</script>

In this example, we use the reactive function to create a reactive data object state, and then register a callback through the watchEffect function Function, this callback function will be called when state.count changes.

When we add a button, the increment function is triggered, and the value of state.count will also change. The watchEffect function will automatically listen for this change and print "count changed to XX" in the console.

As mentioned above, since the watchEffect function relies on reactive data, they will be called immediately as long as the reactive data sends changes.

Benefits of using the watchEffect function

1. No display listener

Using the watchEffect function, we do not need to explicitly call the watch listener to listen for data The change. On the contrary, the watchEffect function automatically tracks dependencies and registers functions with dependencies to ensure data consistency.

2. Better performance

Since the watchEffect function is based on dependency tracking, it can better optimize performance. It automatically cleans up the previous callback and unregisters dependent data so we can create and clean up reactive functionality in one go as needed.

3. Simpler code

Vue3’s responsive system adopts more functional programming ideas, as does the watchEffect function. When reactive data changes, we can write a simple callback to handle it without writing a lot of repetitive code.

Summary

As mentioned above, the watchEffect function is a powerful feature of Vue3, allowing developers to use responsive data and processing more easily and efficiently. Using it can effectively reduce the amount of code we write and optimize the performance of our code.

When you start using Vue3, be sure to learn to use and understand the watchEffect function to take full advantage of Vue3's reactive system.

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