What is the usage of setup in vue3.0

In vue3.0, the setup function is the entrance to the combination API and is used to define data and parameters. The syntax is "setup(props,{slots,attrs,emit}){const name ='name'return {name}}"; this function can only be synchronous and not asynchronous.

The operating environment of this article: Windows 10 system, Vue3 version, DELL G3 computer.

What is the usage of setup in vue3.0

1. Characteristics and functions of setup function

It is certain that Vue3.0 is compatible The Vue2.x version means that we can use the relevant syntax of Vue2.x in Vue3 in our daily work. But when you actually start using Vue3 to write projects, you will find that it is much more convenient than Vue2.x

A major feature function of Vue3---- setup

1. The setup function is a function between the two hook functions of the life cycle function beforeCreate and Created. In other words, data and data cannot be used in the setup function. The data and methods in methods

　2. The setup function is the entrance to the Composition API

　3. The variables and methods defined in the setup function need to be returned in the end. Otherwise, you cannot use it in the template

2. Notes on the setup function:

1. Since the Created life cycle method has not been executed when the setup function is executed, Therefore, in the setup function, the variables and methods of data and methods cannot be used

　2. Since we cannot use data and methods in the setup function, Vue directly replaces the variables and methods in the setup function in order to avoid our incorrect use. this was modified to undefined

3. The setup function can only be synchronous and not asynchronous

Usage 1: Use in combination with ref

<template>
 <div id="app">
  {{name}}
  <p>{{age}}</p>
  <button @click="plusOne()">+</button>
 </div>
</template>
 
<script>
import {ref} from &#39;vue&#39;
export default {
 name:&#39;app&#39;,
 data(){
  return {
   name:&#39;xiaosan&#39;
  }
 },
 setup(){
  const name =ref(&#39;小四&#39;)
  const age=ref(18)
  function plusOne(){
   age.value++ //想改变值或获取值 必须.value
  }
  return { //必须返回 模板中才能使用
   name,age,plusOne
  }
 }
}
</script>

Usage 2: Code splitting

Options API and Composition API

Options API convention:

We need to set the receiving parameters in props

We need to set variables in data

We need to set calculated properties in computed

We need to set listening properties in watch

We need to set event methods in methods

You will find that Options API It has been agreed upon where we should do what, which in turn forces us to split the code to a certain extent.

Now that we use the Composition API, we no longer agree like this. Therefore, the code organization is very flexible. Our control code can be written in the setup.

The setup function provides two parameters, props and context. The important thing is that there is no this in the setup function. In vue3.0, accessing them becomes the following form: this.xxx=》context.xxx

We no longer have this context, and no longer have the forced code separation of the Options API. Composition API gives us a broader world, so we need to be more cautious and constrained.

For complex logic code, we must pay more attention to the original intention of the Composition API, and do not hesitate to use the Composition API to separate the code and cut it into various modules for export.

Our expectation is this:

importuseAfrom'./a';
importuseBfrom'./b';
importuseCfrom'./c';
exportdefault{
setup (props) {
let{ a, methodsA } = useA();
let{ b, methodsB } = useA();
let{ c, methodsC } = useC();
return{
a,
methodsA,
b,
methodsB,
c,
methodsC
}
}
}

Even if the amount of setup content code is getting larger and larger, we will always move forward in a way that is large but not messy and has a clear code structure.

[Related recommendations: "vue.js Tutorial"]

The above is the detailed content of What is the usage of setup in vue3.0. For more information, please follow other related articles on the PHP Chinese website!