1. let 与 const

let 声明的变量只在 let 命令所在的代码块内有效。
const 声明一个只读的常量，一旦声明，常量的值就不能改变。

2.标签模板字符串

    const name ="why"
    const age =18
    //1.基本用法
    //1.1.ES6之前
    //const info = "my name is" + name + ",",age is "+ age
    //1.2.ES6之后
    const info =`my name is ${name}, age is ${age}`
    console.log(info)//my name is why, age is 18

    //2.标签模板字符串的用法
    function foo(...args){
        console.log("参数:",args)
    }
    foo("why",18,1.88)//参数:  ['why', 18, 1.88]
    foo`my name is ${name},age is ${age},height is ${1.88}`//参数: [Array(4), 'why', 18, 1.88]
  

3.ES8 字符串填充方法 padStart padEnd

    const minute ="5".padStart(2,0)
    const second="6".padStart(2,0)
    console.log(`${minute}:${second}`)
    //结果  05:06

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4.ES11，Nullish Coalescing Operator增加了空值合并操作符

    const foo = ""
    const result1 =foo||"默认值"
    const result2 = foo ??"默认值"
    console.log(result1)//默认值
    console.log(result2)//""