lenghth aof array js code example

Example 1: js string contais

const string = "foo";
const substring = "oo";

console.log(string.includes(substring));

Example 2: javascript dedupe array

const names = ['John', 'Paul', 'George', 'Ringo', 'John'];

let x = (names) => names.filter((v,i) => names.indexOf(v) === i)
x(names); // 'John', 'Paul', 'George', 'Ringo'