# How to Remove Duplicate Values from an Array

## filter()

The `filter()` method creates a new array of elements that pass the conditional we provide. In other words, if the element passes and returns `true`, it will be included in the filtered array. And any element that fails or return `false`, it will be NOT be in the filtered array.

let arr = ['html', 'css', 'js', 'css', 'js'];

function removeDuplicates(data) {
   return data.filter((value, index) => arr.indexOf(value) === index);
}

console.log(removeDuplicates(arr));

## forEach()

let arr = ['html', 'css', 'js', 'css', 'js'];

function removeDuplicates(data) {
   let unique = [];
   data.forEach(element => {
      if (!unique.includes(element)) {
         unique.push(element);
      }
   })
   return unique
}

console.log(removeDuplicates(arr));

## reduce()

The `reduce` method is used to reduce the elements of the array and combine them into a final array based on some reducer function that you pass.

let arr = ['html', 'css', 'js', 'css', 'js'];

function removeDuplicates(data) {
   let unique = data.reduce((acc, cur) => {
      if (acc.indexOf(cur) < 0) {
         acc.push(cur);
      }
      return acc;
   }, []);
   return unique;
}

console.log(removeDuplicates(arr));

## Set()

`Set` is a new data object introduced in ES6.
Because `Set` only lets you store unique values. When you pass in an array, it will remove any duplicate values.

let arr = ['html', 'css', 'js', 'css', 'js'];

function removeDuplicates(data) {
   return [...new Set(data)];	
}

console.log(removeDuplicates(arr));

let arr = ['html', 'css', 'js', 'css', 'js'];

console.log(Array.from(new Set(arr)));

## References
- [How to Remove Array Duplicates in ES6](https://medium.com/dailyjs/how-to-remove-array-duplicates-in-es6-5daa8789641c)
- [Performance of Javascript Array Ops](https://blog.usejournal.com/performance-of-javascript-array-ops-2690aed47a50)
- [@webdevofficial](https://www.instagram.com/p/B_fLJCjjQuT/)

###### tags: `JavaScript`