Lifecycle functions in Vue3: Quickly master the lifecycle of Vue3

Vue3 is one of the most popular frameworks in the front-end world, and the life cycle function of Vue3 is a very important part of Vue3. Vue3's life cycle function allows us to trigger specific events at specific times, enhancing the high degree of controllability of components.

This article will explore and explain in detail the basic concepts of Vue3's life cycle functions, the role and usage of each life cycle function, and implementation cases, to help readers quickly master the Vue3 life cycle functions.

1. Basic concepts of Vue3’s life cycle function

Vue3’s life cycle function is a very important part of Vue3 and is a method that is automatically called during component rendering. It allows developers to handle accordingly when components are destroyed, updated, or initialized. Similar to React's life cycle function, Vue3's life cycle function is mainly divided into five stages: "before", "created", "mounted", "updated" and "destroyed".

1. beforeCreate(): This hook function is called after the instance is initialized. Properties such as data and methods have not yet been initialized. The component has not been mounted at this time, so it cannot be used in this hook function. Access to $el.
2. created(): This hook function is called after the instance is created. In this hook function, attributes such as data and methods have been initialized, but $el has not yet been rendered. This hook function is a good place to perform asynchronous requests.
3. beforeMount(): This hook function is called before the component is mounted. During the processing of this hook function, we can modify the DOM node or perform some other initialization work.
4. mounted(): This hook function is called after the component is mounted. It indicates that the component has been rendered and you can start operating the DOM.
5. beforeUpdate(): This hook function is called before the component is updated. In this hook function, some status backup or modification can be performed.
6. updated(): This hook function is called after the component is updated. In this hook function, you can perform some DOM updated operations.
7. beforeUnmount(): This hook function is called before the component is unmounted. In this hook function, you can perform some aftermath work, such as cleaning up timers and so on.
8. unmounted(): This hook function is called after the component is unmounted, indicating that the component has been completely destroyed.

2. The role and usage of each life cycle function

1. beforeCreate()

The beforeCreate() function is called after the instance is initialized. Called, the vue instance has not been created at this time, properties such as data and methods have not been initialized, and the component has not been mounted at this time. So $el cannot be accessed in this hook function.

This hook function is generally used to initialize some important work. For example, in this hook function, you can perform some global configurations, and you can also initialize and set some data or components. This method is very useful and can be used for later Prepare the data for the operation.

A typical usage example:

beforeCreate() {
  console.log('beforeCreate hook!');
}

2. created()

created() hook function is called after the Vue3 instance is created. This The Vue3 instance has been created in the function. In this function, we can access the instance's data and methods, but the page has not yet been rendered.

This hook function is generally used to initialize instances. For example, in this hook function, you can request data, perform some data processing, or perform some plug-in initialization work. This method is very useful and can be used for subsequent Prepare the data for the operation.

A typical usage example:

created() {
  console.log('created hook!');
}

3. beforeMount()

beforeMount() hook function is called before the component is rendered. At this time, the component has been initialized and some operations can be performed in this function. For example, the DOM can be operated in this hook function.

It is generally recommended not to perform time-consuming operations in this hook function, because this may block the first rendering of the DOM.

A typical usage example:

beforeMount() {
  console.log('beforeMount hook!');
}

4. mounted()

The mounted() hook function is called after the component is rendered. In this hook function, we can access the rendered DOM elements and perform some operations. For example, in this hook function, we can obtain the width and height of the element and other information.

A typical usage example:

mounted() {
  console.log('mounted hook!');
}

5. beforeUpdate()

beforeUpdate() hook function is called before the component is updated. In this hook function, some status backup or modification can be performed.

This hook function is generally used in some states that need to be updated. For example, before the component state changes, this hook function is used to back up the state to another place for comparison and verification. At the same time, this hook function can also be used for a series of calculations within a period. For example, the required data can be re-obtained in this hook function.

A typical usage example:

beforeUpdate() {
  console.log('beforeUpdate hook!');
}

6. updated()

这个钩子函数一般用于实现某些需要DOM元素更新后才能进行的操作，例如对比前后数据的信息，需要根据DOM元素的更新来做出相应的处理等。

一个典型的使用示例：

updated() {
  console.log('updated hook!');
}

7. beforeUnmount()

beforeUnmount()钩子函数在Vue3组件卸载之前被调用。在这个钩子函数中，可以进行一些善后的工作，例如清理定时器等等。

一个典型的使用示例：

beforeUnmount() {
  console.log('beforeUnmount hook!');
}

8. unmounted()

unmounted()钩子函数在Vue3组件卸载之后被调用。这个钩子函数表示组件已经被完全销毁。

这个钩子函数用于释放组件占用的内存和资源。

一个典型的使用示例：

unmounted() {
  console.log('unmounted hook!');
}

三、实现案例

在Vue3中实现生命周期函数非常简单，只需在组件中定义对应的函数即可实现。

下面是一个根据生命周期函数实现数据的获取和处理的实现案例：

<template>
  <div>
    <h2>{{ data }}</h2>
  </div>
</template>

<script>
export default {
  data() {
    return {
      data: '',
    };
  },
  beforeCreate() {
    console.log('开始第一步：数据初始化');
    // 进行异步请求，获取数据等操作
    this.data = '数据初始化成功';
  },
  created() {
    console.log('开始第二步：数据处理');
    // 对数据进行处理，例如进行格式化或者加工
    this.data = this.data + '-数据处理成功';
  },
  beforeMount() {
    console.log('开始第三步：准备数据');
    // 渲染组件之前，对数据进行进一步的处理
    this.data = this.data + '-数据准备完成！';
  },
  mounted() {
    console.log('开始第四步：操作DOM');
    // 操作DOM，例如获取元素的宽度或者高度等信息
  },
  beforeUpdate() {
    console.log('开始第五步：备份数据');
    // 对需要更新的状态进行备份，以便进行比较和校验
  },
  updated() {
    console.log('开始第六步：更新状态');
    // 根据DOM更新后的状态进行状态的更新
  },
  beforeUnmount() {
    console.log('开始第七步：清理定时器');
    // 清理组件中的定时器等占用内存的资源
  },
  unmounted() {
    console.log('开始第八步：释放内存');
    // 释放组件中占用的内存和资源
  },
};
</script>

以上实现案例中，我们根据生命周期函数分别进行了数据的初始化、数据的处理、数据的准备、DOM的操作、状态的备份、状态的更新、定时器的清理和内存的释放等八个步骤。

总结

通过本文对Vue3的生命周期函数的探究和讲解，我们可以深入了解和理解每个生命周期函数的作用和使用方法，用于帮助读者深入掌握Vue3的生命周期函数。同时，在实际项目中的应用中，我们也可以根据具体需求，在生命周期函数中实现相应的逻辑，以满足实际需求的业务场景。

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