## 1.变量的声明 ~~~ let a = 10; ~~~ ## 2.块级作用域 ~~~ { let a = 20; } console.log(a); //报错 ~~~ ## 3.例子 ~~~ //es5 function go(){ var x = 1; if(true){ var x = 2; console.log(x); } console.log(x); } go(); ~~~ ~~~ //es6 //两个x，不是同一个变量 function go(){ let x = 1; if(true){ let x = 2; console.log(x); } console.log(x); } go(); ~~~