how to merge two arrays and find the duplicate number in 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: compare two arrays and make sure there are no duplicates js

array1 = array1.filter(val => !array2.includes(val));