How to declare variables in vue.js

Vue.js method of declaring variables: 1. Use let to define, let is a block-level scope. After using let to define the function internally, it has no impact on the outside of the function; 2. Use var to define, and var-defined variables Can be modified; 3. Use const definition, variables defined by const cannot be modified.

The operating environment of this tutorial: Windows 7 system, Vue version 2.9.6, Dell G3 computer.

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vue.js method of declaring variables:

1. Use let to define

let is a block-level scope. After using let to define the function inside, it will have no impact on the outside of the function.

let c = 3;
console.log('函数外let定义c：' + c);//输出c=3
funcion change(){   
    let c = 6;
    console.log('函数内let定义c：' + c);//输出c=6
}
change();
console.log('函数调用后let定义c不受函数内部定义影响：' + c);//输出c=3

2. Use var Definition

Variables defined by var can be modified. If not initialized, undefined will be output and no error will be reported

var a = 1;
// var a;//不会报错
console.log('函数外var定义a:' + a);//可以输出a=1
function change(){  
    a = 4;
    console.log('函数内var定义a:' + a);//可以输出a=4
}
change();
console.log('函数调用后var定义a为函数内部修改值：' + a);//可以输出a=4

3. Use const definition

Variables defined by const cannot be modified and must be initialized

const b = 1;    //正确
const b;    //错误，必须初始化
console.log('函数外const定义b：' +　ｂ);/有输出值
//b = 5;
//console.log('函数外修改const定义b:' + b);//无法输

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