ES5 有全局作用域+函数作用域
for (var i = 0; i < 8; i++) {
var a = 100
}
console.log(a) //100
ES6 增加 块级作用域
1、块级作用域,子级可以访问父级的变量
2、
for (var i = 0; i < 8; i++) {
let a = 100
}
console.log(a) //报错
for (var i = 0; i < 8; i++) {
var a = 100
}
console.log(a) //100
for (var i = 0; i < 8; i++) {
let a = 100
}
console.log(a) //报错