1. 'use strict'; 
    3. {
    4.     let a = 10;
    5.     var b = 1;
    6. }
    7. console.log(a); // Uncaught ReferenceError: a is not defined
    8. console.log(b);
    1. function demo1(argument) {
    2.     var a = [];
    3.     for (var i = 0; i < 10; i++) {
    4.         a[i] = function() {
    5.             console.log(i);
    6.         }
    7.     } 
    8.     a[6](); // var命令 存在变量提升。let不存在变量提升。
    9. }
    11. demo1();