指数运算符（幂） **
console.log(3 ** 2); //9
判断数组中包含 Array.prototype.includes(value)
var arr1 = [1,2,'a','b','c'];
console.log(arr1.includes("a")); //true
console.log(arr1.includes(3)); //false
**console.log(3 ** 2); //9
Array.prototype.includes(value)var arr1 = [1,2,'a','b','c'];
console.log(arr1.includes("a")); //true
console.log(arr1.includes(3)); //false