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

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

Vue3 is the latest version of the Vue framework, and is more powerful and easier to use than Vue2. One of the convenient object property monitoring The function is implemented using defineProperty. This article will explain in detail the usage of defineProperty function and its application in Vue3.

The defineProperty function is a method that comes with JavaScript. It can be used to define a new property on an object or modify an existing property. Its usage is as follows:

Object.defineProperty(obj, prop, descriptor)

Below The meaning of these three parameters are introduced respectively:

• obj: the object whose attributes are to be defined
• prop: the name of the attribute to be defined or modified
• descriptor: definition Or the descriptor of the modified attribute

descriptor is an object containing attribute characteristics, including the following attributes:

• value: the value of the attribute, the default is undefined
• writable: Whether the value of the attribute is writable, the default is false
• enumerable: Whether the attribute is enumerable, the default is false
• configurable: Whether the attribute is configurable, that is, whether it can Modify or delete properties, the default is false

Let’s use an example to understand the usage of defineProperty:

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

In the above example, we defined an empty object obj, And added a name attribute to it, the attribute value is 'Tom', the attribute characteristics are: unmodifiable (writable: false), enumerable (enumerable: true) and non-configurable (configurable: false).

You can see from the console output that the value of obj.name is 'Tom', and after executing obj.name = 'Jerry', the value of obj.name is still 'Tom' in the output result again. Because we set writable to false in the descriptor, that is, the value of this attribute cannot be modified.

So in Vue3, why use defineProperty? The answer is because it can monitor data changes on the page and automatically update the view. Let's take a look at the application in Vue3.

In Vue3, the defineProperty function is encapsulated as a watcher function. The specific usage is as follows:

const obj = {} // 定义一个普通对象
const reactiveObj = reactive(obj) // 通过reactive函数将该普通对象转化为响应式对象

watchEffect(() => {
  console.log(reactiveObj.name)
})
 
setTimeout(() => {
  reactiveObj.name = 'Jerry'
}, 1000)

In the above example, we first define a common object obj, and Convert it into a responsive object through the reactive function, and then use the watchEffect function to monitor changes in the object and output the results.

The setTimeout function is used to modify the name attribute value of the reactiveObj object at intervals. We will find that the output result is also updated after the name attribute value is modified. This is because we listen for changes in the object, so that its changes automatically update the corresponding view.

To sum up, defineProperty is a method that comes with JavaScript. Its use is not cumbersome, but it is very flexible. Especially in the Vue3 framework, the property monitoring function implemented by defineProperty makes it more convenient for us. Complete data monitoring and view update operations efficiently, greatly improving development efficiency.

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