Vue data implements responsiveness

Vue.js is a progressive JavaScript framework for building UI interfaces. Vue.js comes with many powerful features, one of which is reactive data binding.

In traditional front-end development, when data changes, you need to use DOM operations to manually update the view. This method is obviously very cumbersome, so Vue.js provides a data responsive mechanism (Reactivity). Vue.js will automatically monitor data changes and automatically update the interface when the data changes, making it very convenient for us to dynamically update the page.

This article will introduce how to implement responsive data in Vue.js, and discuss its principles and applications.

What is responsive data

In Vue.js, we usually use the data option to define the data of the component. For example:

export default {
  name: 'MyComponent',
  data() {
    return {
      message: 'Hello, Vue!',
    };
  },
}

In the above code, we use the data option to define a data named message, with the initial value being 'Hello, Vue! '. Now, if we modify the value of message in the component, for example:

this.message = 'Hello, World!';

Vue.js will automatically update the interface and change the text displayed in the view from 'Hello, Vue! ' becomes 'Hello, World!'.

This mechanism for automatically updating views is the responsive data mechanism of Vue.js. When we modify the data, Vue.js will automatically detect the changes in this data and update the representation of this data in the view.

How to implement responsive data

The core principle of Vue.js to implement responsive data is to hijack the setter and getter functions of data through the Object.defineProperty() method.

When we get the value of a Reactive data property, the getter function will be called, so that Vue.js will know that you want to access this data.

When we set the value of a Reactive data property, the setter function will be called, so that Vue.js will know that the data is ready to be modified and perform corresponding update operations.

For example, the message data in the above example is roughly processed internally by Vue.js:

// 定义数据
let data = { message: 'Hello, Vue!' };

// 转化为响应式数据
Object.defineProperty(data, 'message', {
  get() {
    // 当获取 message 的值时，返回 data 中 message 对应的值
    return this._message;
  },
  set(value) {
    // 当设置 message 的值时，同时更新 data 中 message 对应的值，并更新视图
    this._message = value;
    updateView();
  },
});

// 修改数据
data.message = 'Hello, World!'; // 触发 setter 函数，更新 data 和视图

Through the Object.defineProperty() method , we define a Reactive data property named message. When getting the value of this property, Vue.js will call the get() function. When setting the value of this property, Vue.js will call the set() function.

In this way, we get a responsive data that can be automatically updated.

Application of responsive data

The responsive data mechanism brings many benefits to Vue.js. We can directly modify data in the component without manually calling DOM operations, thus improving development efficiency and development experience.

In addition to this, reactive data supports various advanced features such as computed properties and listeners.

Computed properties

Computed properties refer to defining a property in a component. The value of this property is not obtained directly from data, but needs to be calculated. The benefit of computed properties is that they can cache calculation results and automatically update when the calculated object changes.

For example:

export default {
  name: 'MyComponent',
  data() {
    return {
      firstName: '',
      lastName: '',
    };
  },
  computed: {
    fullName() {
      return this.firstName + ' ' + this.lastName;
    },
  },
}

In the above code, we define a calculated property named fullName through computed. This property will automatically calculate the current full name based on the expression this.firstName ' ' this.lastName instead of getting it from data.

If we modify the value of firstName or lastName, the fullName property will automatically recalculate and update the interface without us manually Call the update method.

Listener

Listener refers to defining a listening function in the component. This listening function will be automatically triggered when a certain data changes, thereby completing some useful operations.

For example:

export default {
  name: 'MyComponent',
  data() {
    return {
      message: '',
    };
  },
  watch: {
    message(newVal, oldVal) {
      // 监听 message 变化，做相应的处理
    },
  },
}

In the above code, we define a listener named message through watch. This listener will be automatically triggered when the value of message changes, so that specific operations can be completed.

For example, in some cases, we need to send a request to the server to update the data when message changes. At this time, we can monitor message changes in watch and complete the request operation in the callback function.

Summary

The responsive data mechanism of Vue.js is one of its core functions, which allows us to easily implement automatic updates of data and views. In Vue.js, we use data to define reactive data, and use advanced features such as computed properties and listeners to further extend the functionality of data binding.

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