Filter Out Non-Unique Values in JavaScript

We have an array of literals that contains some duplicate values appearing for many times like this −

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

We are required to write a JavaScript function that takes in this array and pick out all the duplicate entries from the original array and only once.

Therefore, for the above array, the output should be −

const output = [1, 4, 3, 2];

Example

The code for this will be −

const arr = [1, 4, 3, 3, 1, 3, 2, 4, 2, 1, 4, 4];
const removeDuplicate = arr => {
   const res = [];
   for(let i = 0; i < arr.length; i++){
      if(arr.indexOf(arr[i]) !== arr.lastIndexOf(arr[i])){
         if(!res.includes(arr[i])){
            res.push(arr[i]);
         };
      };
   };
   return res;
};
console.log(removeDuplicate(arr));

Output

The output in the console −

[1, 4, 3, 2]