Removing Array Dublicates in ES6

Here are 4 ways to filter out duplicates from an array and return only the unique values.

1. Set#

Set is one of the cool thing happening in ES6. It's a new data structure that store unique values of any type. You can iterate through the elements of a set in insertion order. A value in the Set may only occur once; it is unique in the Set's collection.

const array = ['🦄', 1, 2, '🦄', '🦄', 3, 2]

[...new Set(array)]

// ['🦄', 1, 2, 3];

2. Filter#

The filter() method creates a new array with all elements that pass the test implemented by the provided function.

const array = ['🦄', 1, 2, '🦄', '🦄', 3, 2]

array.filter((item, index) => array.indexOf(item) === index)

// ['🦄', 1, 2, 3];

Retrieve the duplicate values#

const array = ['🦄', 1, 2, '🦄', '🦄', 3, 2]

array.filter((item, index) => array.indexOf(item) !== index)

// ['🦄','🦄', 2]

3. Reduce#

In order to understand this option, let's understand what these two methods are doing: reduce and includes.

.reduce()#

The reduce() method executes a reducer function (that you provide) on each member of the array resulting in a single output value.

const array = ['🦄', 1, 2, '🦄', '🦄', 3, 2]

array.reduce((unique, item) => (unique.includes(item) ? unique : [...unique, item]), [])

// ['🦄', 1, 2, 3];

.includes()#

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

const array = ['🦄', 1, 2, '🦄', '🦄', 3, 2]

array.includes('🦄') // true
array.includes('3') // true
array.includes('23') // false

4. lodash#

const array = ['🦄', 1, 2, '🦄', '🦄', 3, 2]

_.uniq(array)

// ['🦄', 1, 2, 3];

Do not forget: The bundle size for lodash@4.17.11 is 24.2kB (minified + gzipped). See here