how to compare two elements of array in javascript searchin duplicates code example

Example 1: how to get duplicate values from array in javascript

var array = [1, 2, 2, 3, 3, 4, 5, 6, 2, 3, 7, 8, 5, 22, 1, 2, 511, 12, 50, 22];

console.log([...new Set(
  array.filter((value, index, self) => self.indexOf(value) !== index))]
);

Example 2: function that duplicates data in array js

function doubleValues(array) {
  var newArray = [];
  array.forEach(function (el) { newArray.push(el, el); });    
  return newArray;
}

console.log(doubleValues([1,2,3]));