JSFiddle - React, Tailwind, and code Playground

by Sunny SM

JavaScript

function getDuplicates(arr) {
	const sorted_arr = arr.slice().sort();
	const results = [];
	for (var i = 0; i < sorted_arr.length - 1; i++) {
    if (sorted_arr[i + 1] === sorted_arr[i]) {
        results.push(sorted_arr[i]);
    }
	}

  return results;
}

alert(getDuplicates([1, 3, 21, 103, 21, 4, 3, 1, 4, 0]))
// [1, 21]