Make an array of another array's duplicate values in JavaScript

We are required to write a JavaScript function that takes in an array of literals. The function should prepare a new array of all those elements from the original array that are not unique (duplicate elements.)

For example −

If the input array is −

const arr = [3, 6, 7, 5, 3];

Then the output should be −

const output = [3];

Example

The code for this will be −

const arr = [3, 6, 7, 5, 3];
const makeDuplicatesArray = (arr = []) => {
   const res = [];
   for(let i = 0; i < arr.length; i++){
      if(i === arr.lastIndexOf(arr[i])){
         continue;
      };
      res.push(arr[i])
   };
return res;
};
console.log(makeDuplicatesArray(arr));

Output

And the output in the console will be −

[3]