## let ### 块级作用域 ``` { var d = 0; let e = 3; } console.log(d) console.log(e) ``` ### 不能重复申明 ``` var f = 1; var f = 2; console.log(f) //2 let g = 3; let g = 4; console.log(g) //错误 ``` ### 不会申明提前 ``` console.log(b) //undefined console.log(c) //报错 var b = 1; let c = 2; ```