for loop js find duplicate numbers code example

Example 1: javascript get duplicates in array

function getDuplicateArrayElements(arr){
    var sorted_arr = arr.slice().sort();
    var 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;
}

var colors = ["red","orange","blue","green","red","blue"];
var duplicateColors= getDuplicateArrayElements(colors);//["blue", "red"]

Example 2: how to get duplicate values from array in javascript

const arr = ["q", "w", "w", "e", "i", "u", "r"]
arr.reduce((acc, cur) => { 
  if(acc[cur]) {
    acc.duplicates.push(cur)
  } else {
    acc[cur] = true //anything could go here
  }
}, { duplicates: [] })