Let's talk about the implementation mechanism of Vue data binding

Vue.js is a modern JavaScript framework, one of the most important features is two-way data binding. It means that when the data changes, the view will automatically update, and when the view changes, the data will also automatically update. This feature brings great convenience to developers, allowing us to focus more on the implementation of business logic instead of constantly manually updating views and data. In Vue, the implementation mechanism of data binding has the following aspects:

1. Responsive object

The reactive implementation in Vue is by defining a reactive object. Mark certain properties on an object as monitorable. When these properties change, Vue updates the related views. The specific implementation uses the Object.defineProperty method of ES5 to hijack the getter and setter methods of the property.

First, we define a simple template. The template contains an input and a span element. The value attribute of the input and the textContent attribute of the span are data bound:

<div>
  <label>输入内容：</label>
  <input>
  <p>输出内容：{{ message }}</p>
</div>

Then We define a reactive object in JavaScript:

var vm = new Vue({
  el: '#app',
  data: {
    message: 'Hello Vue!'
  }
})

When executing this code, Vue parses the instructions in the template, marks the message property as a reactive property, and then uses the Object.defineProperty method to set its getter and The setter method is hijacked to automatically update the corresponding view when the message attribute changes.

2. Template compilation

In Vue.js, when a Vue instance is created, Vue will parse the instructions in the template and generate a DOM rendering function, and then pass this DOM Render function to generate real DOM elements.

The template in Vue.js is actually HTML code. Vue can parse the HTML code into an AST abstract syntax tree, generate the corresponding vnode through static analysis of the abstract syntax tree, and then generate DOM rendering based on the vnode. function.

For example, in the template code mentioned above, Vue will parse it into the following abstract syntax tree:

{
  type: 'element',
  tag: 'div',
  attrsList: [],
  attrsMap: {},
  children: [
    {
      type: 'element',
      tag: 'label',
      attrsList: [],
      attrsMap: {},
      children: [
        {
          type: 'text',
          text: '输入内容：'
        }
      ]
    },
    {
      type: 'element',
      tag: 'input',
      attrsList: [
        {
          name: 'v-model',
          value: 'message'
        }
      ],
      attrsMap: {
        'v-model': 'message'
      },
      children: []
    },
    {
      type: 'element',
      tag: 'p',
      attrsList: [],
      attrsMap: {},
      children: [
        {
          type: 'text',
          text: '输出内容：'
        },
        {
          type: 'expression',
          text: '_s(message)',
          tokens: [
            { '@binding': 'message' }
          ]
        }
      ]
    }
  ]
}

The v-model directive binds the message attribute to the value attribute of the input element. is determined, and {{ message }} binds the message attribute to the textContent attribute of the p element.

3. Implementation of components

In Vue, components are one of the important concepts. Components allow us to split the application into small, reusable parts, which can effectively improve the reusability and maintainability of the code.

The implementation of components is also inseparable from the data binding mechanism. Inside the component, we can use the props provided by Vue to define the properties of the component, and then use these properties inside the component to achieve two-way binding of data.

For example, we define a simple component:

Vue.component('my-component', {
  props: ['title'],
  template: '<h1 id="title">{{ title }}</h1>'
})

Then use this component in the template:

<my-component></my-component>

In the template, we pass in an attribute title to the component, Inside the component, the title attribute is defined and used through props.

Summary:

The mechanism of Vue.js to implement data binding is to use responsive objects, template compilation and component implementation. By defining responsive objects and hijacking getter and setter methods, and parsing templates to generate DOM rendering functions, automatic data updates are achieved. Inside the component, we define the properties of the component through props and use these properties to implement two-way binding of data. This series of mechanisms makes Vue.js a modern JavaScript framework and provides developers with a good development experience and convenience.

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