JSFiddle - React, Tailwind, and code Playground

by Sergei Marochkin

JavaScript

const elements = [1,2,3,2,1,5,6,5,5,5, 534, 534, 43534,534, 3534543];


const duplicates = [];

for (let i = 0; i < elements.length; i += 1) {
  for (let j = i + 1; j < elements.length; j += 1) {
    if (elements[i] === elements[j] && !duplicates.includes(elements[i])) {
      duplicates.push(elements[i]);
    }
  }
}


console.log(duplicates);