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JS Coding Question #4: Remove Duplicates [Common Question]

Interview Question #4:

Write a function that will remove duplicate in an array❓🤔 You can get a variation of this question as Get unique characters from a list.

If you need practice, try to solve this on your own. I have included 2 potential solutions below.

Note: There are many other potential solutions to this problem.

Feel free to bookmark 🔖 even if you don't need this for now. You may need to refresh/review down the road when it is time for you to look for a new role.


Solution #1: ES6 Set

  • uses the elegance of Set just like other programming languages. A value in the Set may only occur once; it is unique in the Set's collection.
function removeDuplicates(array) {
  return [ Set(array)]
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Solution #2: Object

  • below will use a js plain object to store key value pairs. Value can be other values as well, i chose to increment it so we may use it for other purpose like get the total count for a characters, etc.
function removeDuplicates(array) {
  const map = {}

  for (const char of array) {
    if (map[char]) {
    } else {
       map[char] = 1

  return Object.keys(map)
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Top comments (2)

machinecode0101 profile image
Matin • Edited

Hi, great solutions! I think the question could be more clear 😁 since this code doesn't remove the duplicates!!! it just creates a new array but without the duplicates!!!!

Thanks anyways for these JS questions, they make me think more methodically!!

frontendengineer profile image
Let's Code

you are welcome! Creating new array typically an engineer would want to prevent unexpected side effects or bugs.