best way to find duplicates in an array code example

Example 1: find duplicate values in array javascript

const findDuplicates = (arr) => {
  let sorted_arr = arr.slice().sort(); // You can define the comparing function here. 
  // JS by default uses a crappy string compare.
  // (we use slice to clone the array so the
  // original array won't be modified)
  let results = [];
  for (let i = 0; i < sorted_arr.length - 1; i++) {
    if (sorted_arr[i + 1] == sorted_arr[i]) {
      results.push(sorted_arr[i]);
    }
  }
  return results;
}

let duplicatedArray = [9, 4, 111, 2, 3, 4, 9, 5, 7];
console.log(`The duplicates in ${duplicatedArray} are ${findDuplicates(duplicatedArray)}`);

Example 2: find-array-duplicates

npm i find-array-duplicates

import duplicates from 'find-array-duplicates'

const names = [
 { 'age': 36, 'name': 'Bob' },
 { 'age': 40, 'name': 'Harry' },
 { 'age': 1,  'name': 'Bob' }
]
 
duplicates(names, 'name').single()
// => { 'age': 36, 'name': 'Bob' }