ES6新增的let与const

1、const

声明常量，一旦声明必须立马赋值，否则报错

const PI = 3.14

const PI;
//报错：Uncaught SyntaxError: Missing initializer in const declaration

常量赋值以后，不能改变，否则同样报错

const PI = 3.14 ;
PI = 3;
//报错：Uncaught TypeError: Assignment to constant variable.

2、let

声明的变量只在let命令所在的代码块内有效

for(let i=0 ;i<3;i++){
    console.log(i)
}
console.log(i)
//报错：Uncaught ReferenceError: i is not defined

 

转载于:https://www.cnblogs.com/lhyhappy365/p/8426542.html