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FKit (pronounced eff-kit) is a functional programming toolkit for JavaScript. It provides many functions for solving common problems with functions, objects, arrays, and strings. It aims to provide reusable building blocks while maintaining a laser focus on everyday utility.


Table of Contents

Getting Started


The quickest and easiest way to start using FKit is to include a reference to the minified file in the head of your HTML file.

You can always grab the latest version with:

<script src=""></script>

You can also use a specific version with:

<script src=""></script>


Install the npm package:

> npm install fkit

Require it in your code:

var F = require('fkit')
console.log(F.add(1, 2))

Or, if you are using ES6 modules, you can import just the bits you want:

import {add} from 'fkit'
console.log(add(1, 2))



// Sum the numbers in a list.
F.sum([1, 2, 3]) // 6

// Stash a string.'{', '}'), 'hello') // '{h}{e}{l}{l}{o}'

// Intersperse the numbers in a list with another number.
F.intersperse(4, [1, 2, 3]) // [1, 4, 2, 4, 3]

// Filter the numbers in a list where 1 <= n <= 5.
[1, 2, 3, 4, 5].filter(F.between(2, 4)) // [2, 3, 4]

// Calculate the cartesian product of two lists.
F.cartesian([1, 2], [3, 4]) // [[1, 3], [1, 4], [2, 3], [2, 4]]

// Calculate the permutations of a list.
F.permutations('abc') // ['abc', 'bac', 'cba', 'bca', 'cab', 'acb']

Check out some more examples:


FKit is licensed under the MIT licence. See the LICENCE file for more details.