ES6中变量和常量定义之后,可以防止重复再定义
- ES5语法:
var a = 1;
var a = 2;
alert(a); // 2
- ES6语法:
let a = 1;
let a = 2;
alert(a); // 报错 Uncaught SyntaxError: Identifier 'a' has already been declared
var a = 1;
var a = 2;
alert(a); // 2
let a = 1;
let a = 2;
alert(a); // 报错 Uncaught SyntaxError: Identifier 'a' has already been declared