skip to content

// search
Repeated array values passing through a filter and emerging as unique shapes

// tutorials

Remove Duplicates from a JavaScript Array

By Pankaj Sanam

1 min read

#javascript #es6 #es2015

This is one of the questions that I used to ask in interviews. I was also asked this question initially when I started my career as a software engineer.

It’s a very simple problem yet surprisingly many fails to answer it. I know because I have asked many candidates and not all of them were able to answer correctly.

There are many ways to do this. So let’s take a look at the different ways to do it one by one:

Using Set (My favorite way)

It is the shortest way to achieve this:

const colors = ["red", "blue", "green", "red", "blue"];


console.log([...new Set(colors)]);

Using indexOf() and loop

const colors = ["red", "blue", "green", "red", "blue"];


const uniqueColors = [];


for (let color of colors) {
  if (uniqueColors.indexOf(color) === -1) {
    uniqueColors.push(color);
  }
}


console.log(uniqueColors);

Using indexOf() and filter

const colors = ["red", "blue", "green", "red", "blue"];


const uniqueColors = colors.filter(
  (color, index) => colors.indexOf(color) === index,
);


console.log(uniqueColors);

Using forEach() and include()

const colors = ["red", "blue", "green", "red", "blue"];


const uniqueColors = [];


colors.forEach((color) => {
  if (!uniqueColors.includes(color)) {
    uniqueColors.push(color);
  }
});


console.log(uniqueColors);

I hope this was useful for you!

Thanks for reading!