Es7相关

一:Array.prototype.includes():
之前的方法:indexOf,find,for循环遍历
判断数组中是否包含自定元素.(只能判断基本数据类型)

let arr = ['a', 'b', 'c']
console.log(arr.includes('a'));//true
console.log(arr.includes('b',2));//第二个参数,开始查找的位置
console.log(arr.includes('d'));//false

与index of的区别:

//都只能判断基本数据类型,基本数据类型严格执行 ===
 let arr = [1,2,[3,4],5,NaN];
 console.log(arr.includes([3,4]));//false
 console.log(arr.indexOf([3,4]));//-1
 console.log(arr.includes('2'));//false
 console.log(arr.indexOf('2'));//-1
//includes 可以判断是否存在NaN,indexof 不可以
 console.log(arr.includes(NaN));//true
 console.log(arr.indexOf(NaN));//-1
//inedxof会返回存在的索引
 console.log(arr.indexOf(2));//1

二:幂运算符

function com(x, y) {
    let result = 1;
    for (let i = 0; i < y; i++) {
        result *= x;
    }
    return result;
}
console.log(com(2,3));//8
Math.pow(2,2) //4

2**2//4