js for loop find duplicate code example

Example 1: javascript duplicate an array

let arr =["a","b","c"];
// ES6 way
const duplicate = [...arr];

// older method
const duplicate = Array.from(arr);

Example 2: check for duplicates in array javascript

[1, 2, 3].every((e, i, a) => a.indexOf(e) === i) // true

[1, 2, 1].every((e, i, a) => a.indexOf(e) === i) // false