ES6中includes

1、判断字符串中是否存在指定字符
console.log('abc'.includes(a,0)) //true,从索引值0开始看是否存在a
console.log('abc'.includes(a,1)) //false
console.log('abc'.includes(ab,0)) //true
console.log('abc'.includes(ac,0))//false

2、判断数组中是否含有某个成员
console.log([1,2,3].includes(1,0))//从索引值0开始判断是否含有成员1