How does Vue implement hook functions and life cycle management?

Vue is a popular JavaScript framework that provides some special mechanisms so that components can be easily managed, modified and manipulated. One of the important mechanisms is hook functions and life cycle management. This article will introduce the concepts of hook functions and life cycles in Vue and discuss how to implement them.

1. What are hook functions and life cycles?

In Vue, every component has a life cycle. The life cycle is the process that a component goes through in various stages. Vue divides the component's life cycle into different stages, and performs specific operations at each stage. These operations are called hook functions in Vue.

Hook functions are specific methods that are executed at various stages of the component life cycle. In Vue, hook functions can help us perform some operations in different life cycle stages of components. This makes it easier to manage the component's behavior.

2. Different stages of Vue life cycle

Vue’s life cycle can be divided into 8 different stages:

• beforeCreate
• created
• beforeMount
• mounted
• beforeUpdate
• updated
• beforeDestroy
• destroyed

In the life cycle of the Vue component, each stage has a corresponding hook function that can perform specific operations at a specific point in time. The following is a detailed introduction to each stage and its corresponding life cycle function:

• beforeCreate: Called before the instance is initialized. At this point the instance's properties have not been initialized, so data and computed properties cannot be accessed at this stage.
• created: The instance has been created and the data has been initialized, but the DOM has not yet been mounted. At this point the data and computed properties can be accessed, but the DOM nodes cannot be obtained.
• beforeMount: The DOM has been mounted but has not yet been rendered. At this point, DOM nodes and component instances can be obtained.
• mounted: The DOM has been mounted and rendered. At this time, you can access the DOM node and perform operations similar to jQuery. It is best to use custom hooks to listen to various events of the DOM node at this stage.
• beforeUpdate: The data has changed, but the DOM has not yet been re-rendered. At this time, you can modify the data, but do not trigger status updates.
• updated: The data has been updated and the DOM has been re-rendered. Data can be modified, but status updates should not be triggered.
• beforeDestroy: The instance is about to be destroyed. Cleanup work can be done here, such as clearing timers, etc.
• destroyed: The instance has been destroyed. At this time, cleanup work needs to be performed, such as clearing event listeners, etc.

3. How to use hook functions and life cycles?

In Vue, you can use the officially provided API to define the hook function of the component. In the options of a Vue instance or component, you can define hook functions at different stages:

var vm = new Vue({
  el: '#app',
  data: {
    message: ''
  },
  beforeCreate: function () {
    console.log('beforeCreate !')
  },
  created: function () {
    console.log('created !')
  },
  beforeMount: function () {
    console.log('beforeMount !')
  },
  mounted: function () {
    console.log('mounted !')
  },
  beforeUpdate: function () {
    console.log('beforeUpdate !')
  },
  updated: function () {
    console.log('updated !')
  },
  beforeDestroy: function () {
    console.log('beforeDestroy !')
  },
  destroyed: function () {
    console.log('destroyed !')
  }
})

Hook functions will be automatically called at different stages of the instance's life cycle. In this way, the instance can be operated at a specific point in time and the components can be managed more conveniently. For example, you can request data in the created hook function, modify the DOM node in the mounted hook function, clean up the work in the beforeDestroy hook function, etc.

In addition, you can also define hook functions in components. The hook function of a component is very similar to the hook function of an instance and can be automatically called and perform specific operations:

Vue.component('my-component', {
  template: '<div>My Component</div>',
  beforeCreate: function () {
    console.log('beforeCreate !')
  },
  created: function () {
    console.log('created !')
  },
  beforeMount: function () {
    console.log('beforeMount !')
  },
  mounted: function () {
    console.log('mounted !')
  },
  beforeUpdate: function () {
    console.log('beforeUpdate !')
  },
  updated: function () {
    console.log('updated !')
  },
  beforeDestroy: function () {
    console.log('beforeDestroy !')
  },
  destroyed: function () {
    console.log('destroyed !')
  }
})

If you need to encapsulate a component, you can also use mixin extensions in the component, and the mixin will be used in the component's life. Automatically call the hook function during the cycle:

var mixin = {
  beforeCreate: function () {
    console.log('beforeCreate !')
  },
  created: function () {
    console.log('created !')
  },
  beforeMount: function () {
    console.log('beforeMount !')
  },
  mounted: function () {
    console.log('mounted !')
  },
  beforeUpdate: function () {
    console.log('beforeUpdate !')
  },
  updated: function () {
    console.log('updated !')
  },
  beforeDestroy: function () {
    console.log('beforeDestroy !')
  },
  destroyed: function () {
    console.log('destroyed !')
  }
};

Vue.component('my-component', {
  mixins: [mixin],
  template: '<div>My Component</div>'
})

4. Summary

The hook function and life cycle in Vue provide a convenient mechanism for the management and operation of components. During the component's life cycle, you can define hook functions to perform specific operations. Hook functions can be defined in the options of the Vue instance or component, or in the component using mixin extensions. In this way, we can more accurately control the behavior of components and make it easier to manage and modify components.

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