Extract unique values from an array - JavaScript

Suppose we have an array that contains duplicate elements like this −

const arr = [1,1,2,2,3,4,4,5];

We are required to write a JavaScript function that takes in one such array and returns a new array. The array should only contain the elements that only appear once in the original array.


Following is the code −

const arr = [1,1,2,2,3,4,4,5];
const extractUnique = arr => {
   const res = [];
   for(let i = 0; i < arr.length; i++){
      if(arr.lastIndexOf(arr[i]) !== arr.indexOf(arr[i])){
   return res;


This will produce the following output in console −

[ 3, 5 ]

Updated on: 30-Sep-2020

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