Detailed explanation of defineProperty function in Vue3: convenient object property monitoring

Detailed explanation of the defineProperty function in Vue3: Convenient object property monitoring

Vue3, as the latest version of the Vue framework, has many other new features in addition to the reconstruction of responsive data. Among them, defineProperty, the API for defining object properties, has also undergone some optimizations. This article will explain in detail the defineProperty function in Vue3 and its practical use cases.

The basic concept of defineProperty function

defineProperty is a function in the JavaScript native API. It can define a new property on an object or modify an existing property. When a new property is defined, we can specify some of its characteristics, such as whether it is enumerable, whether it can be modified, etc.

In Vue3, the defineProperty function has been improved, its syntax and usage are more flexible, and it can be more conveniently used to monitor changes in object properties.

Syntax

In Vue3, we can call the defineProperty function in the following way:

Object.defineProperty(obj, prop, descriptor)

• obj: The object on which the property is to be defined.
• prop: The name of the property to be defined or modified.
• descriptor: Descriptor of the attribute to be defined or modified.

For example, we can define an object property like this:

let obj = {}
Object.defineProperty(obj, 'nickName', {
  value: 'Bobo',
  writable: false,
  enumerable: true,
  configurable: false
})
console.log(obj.nickName)
// 'Bobo'

In this example, we define an attribute nickName on the obj object through the defineProperty function. The value attribute specifies that the default value of this attribute is 'Bobo', the writable attribute specifies that this attribute cannot be changed, the enumerable attribute specifies that this attribute is enumerable, and the configurable attribute specifies that this attribute cannot be deleted.

As mentioned above, the syntax of this API looks a bit verbose and unintuitive, which is one of the improvements made by Vue3.

Improvements of defineProperty function in Vue3

Let us first take a look at how defineProperty is used to monitor object property changes in Vue2:

let obj = {
  age: 40
}
Object.defineProperty(obj, 'age', {
  get() {
    console.log('get age:', this._age)
    return this._age
  },
  set(newAge) {
    console.log('set age:', newAge)
    this._age = newAge
  }
})
obj.age = 30
console.log(obj.age)
// 'set age: 30'
// 'get age: 30'
// 30

In this example, we An age attribute is defined on the obj object. We define its get and set methods and put them in the descriptor parameter and pass them to the defineProperty function. Here, we also use an internal member variable _age to store the actual value of the age attribute.

When we modify the age attribute through obj.age=30, the set method is called, the console outputs 'set age: 30', and the value of _age is modified. When we subsequently access the age attribute, the get method is called, the console outputs 'get age: 30', and the value of _age is returned.

Vue3 improves the defineProperty function in two main aspects:

1. For monitoring of the entire object, the syntax is more concise

In Vue3, we You can pass the object directly to the reactive function, and all properties in the object will be listened to. Of course, you can also use Vue2 style writing. The following example:

Vue2写法：
const obj = { age: 40 }
const reactiveObj = Vue.reactive(obj)
console.log(reactiveObj.age) // 40

Vue3写法：
const obj = { age: 40 }
const reactiveObj = reactive(obj)
console.log(reactiveObj.age) // 40

We will find that the writing method of Vue3 uses a new reactive function to replace the Vue.reactive function in Vue2, which eliminates the need for explicit calls to defineProperty and makes the syntax more concise. .

2. For monitoring a single property, use the ref function

In Vue3, for monitoring a single property, we can use the ref function to monitor its changes.

const age = ref(40)
console.log(age.value) // 40

We don’t need to explicitly call the defineProperty function, we only need to call the ref function to listen. At this time, the age object has get and set methods similar to those defined in Vue2. These methods can be triggered when we access or change the value attribute.

Summary

The defineProperty function is a very useful tool in the JavaScript native API. Vue3 has modified it to make it more convenient to monitor changes in object properties. Although the usage of this API seems a bit verbose, it is very powerful and can help us convert an ordinary object into a responsive data object.

As we have seen in Vue3, now we no longer need to explicitly use the defineProperty function to monitor object properties. The new API officially provided by Vue3 allows us to complete this more conveniently and flexibly. class operations. Of course, if you want to use the defineProperty function directly, you can also continue to use it like Vue2.

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