Utilities for working with functions in JavaScript, with TypeScript.

(Inspired by functools of the same name)

npm install functools --save

Always returns the same value supplied to it.

identity(42); //=> 42

Returns a function that always returns the same value supplied to it.

identity(42); //=> 42

Optimize a function to speed up consecutive calls by caching the result of calls with identical input arguments. The cache can be overridden for features such as an LRU cache.

let i = 0;
const fn = memoize(() => ++i);

fn("foo"); //=> 1
fn("foo"); //=> 1

fn("bar"); //=> 2
fn("bar"); //=> 2

Memoize the result of fn after the first invocation.

let i = 0;
const fn = memoize0(() => ++i);

fn(); // => 1
fn(); // => 1
fn(); // => 1

Memoize the result of a function based on the most recent arguments.

let i = 0;
const fn = memoize(() => ++i);

fn("foo"); //=> 1
fn("foo"); //=> 1

fn("bar"); //=> 2
fn("bar"); //=> 2

fn("foo"); //=> 3
fn("foo"); //=> 3

Return a function that fetches key from its operand.

prop("foo")({ foo: 123 }); //=> 123

Return a function that calls the method name on its operand. If additional arguments are given, they will be given to the method as well.

invoke("add", 5, 5)({ add: (a, b) => a + b }); //=> 10

Wrap a function to rate-limit the function executions to once every ms milliseconds.

let i = 0
const fn = throttle(() => ++i, 100)

fn() // i == 1
fn() // i == 1
fn() // i == 1

setTimeout(() => /* i == 2 */, 200)

Tip: Use fn.clear and fn.flush for finer execution control.

• fn.clear Unconditionally clears the current timeout
• fn.flush When fn is pending, executes fn() and starts a new interval

Given a fn, return a wrapper that accepts an array of fn arguments.

Promise.all([1, 2, 3]).then(spread(add));

Flip a binary fn argument order.

flip(subtract)(5, 10); //=> 5

Returns a partially applied fn with the supplied arguments.

partial(subtract, 10)(5); //=> 5

Left-to-right function composition.

sequence(partial(add, 10), partial(multiply, 5))(5); //=> 75

Right-to-left function composition.

compose(partial(add, 10), partial(multiply, 5))(5); //=> 35

Fix the number of receivable arguments in origFn to n.

["1", "2", "3"].map(nary(1, fn)); //=> [1, 2, 3]

This module uses TypeScript and publishes type definitions on NPM.

Apache 2.0