1. 字符串

es5：

  1. indexOf()
var str = "123"
console.log(str.indexOf("2") !== -1); // true

es6：

  1. includes()
let string = "apple,banana,orange";
string.includes("banana");     // true

2. 数组

es5：

  1. indexOf()
var arr = [1, 2, 3]
console.log(arr.indexOf(2) !== -1); // true

es6：

  1. includes()
let string = ["apple", "banana", "orange"];
string.includes("banana");     // true