此处let与var区别

Question

var a = 2;

(function IIFE(global){

    var a =3

    console.log(a)//3

    console.log(global.a)//2

})(window);

console.log(a);//2

let a = 2;

(function IIFE(global){

    var a =3

    console.log(a)//3

    console.log(global.a)//undefine   为什么变成undefined

})(window);

console.log(a);//2

Answer 1

let const即便在全局环境中定义变量也不会绑定到window对象上可以找本基础的书看看