es7 and es8

js

es7新增加了两个新属性：
1)Array.prototype.includes

let arr = [1,2,3,4];
arr.includes(2)   //true

2)幂运算 **

let a = 2;
console.log(a**3) //8 

es8新增的属性有：
1)允许结尾逗号

let obj = {
    a,
    b,
    c,
}

2)Object.entries Object.values

Object.entries({foo:1,bar:2})  // [['foo':1],['bar':2]]  
Object.values({foo:1,bar:2})   // [1,2]

3)字符串填充 padStart padEnd trimStart trimEend

console.log('testing'.padStart(12).length)  //'  testing'
console.log('testing).padStart(12, '_')   //'______testing'