let、const、class声明的变量不属于顶层对象★

const USER_NAME = "wangzz";
class A {}
let age = 25;
var job = "coder";
 
function printInfo() {
    console.log("USER_NAME: ", this.USER_NAME);
    console.log("age: ", this.age);
    console.log("class A", this.A);
    console.log("job: ", this.job);
}
 
printInfo()
// USER_NAME:  undefined
// age:  undefined
// class A undefined
// job:  coder

ES6规定，var命令和function命令声明的全局变量，是顶层对象的属性，但是let、const、class命令声明的全局变量不属于顶层对象的属性