array concat without duplicates javascript code example

Example 1: merge array no duiplicates js

let array1 = ['a','b','c'];
let array2 = ['c','c','d','e'];
let array3 = array1.concat(array2);
array3 = [...new Set([...array1,...array2])]; // O(n)

Example 2: javascript create array with repeated values

Array(5).fill(2)
//=> [2, 2, 2, 2, 2]