functools

Functools

Utilities for working with functions in JavaScript, with TypeScript.

(Inspired by functools of the same name)

Installation

npm install functools --save

Usage

identity<T>(arg: T) => T

Always returns the same value that was used as the argument.

identity(42) //=> 42

memoize<T, U>(fn: (x: T) => U, cache?: Cache) => (x: T) => U

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

See also: memoize0 for zero-length function arguments.

prop<K>(key: K) => (obj: T) => T[K]

Return a function that fetches key from its operand.

prop('foo')({ foo: 123 }) //=> 123

invoke<K, A, T>(key: K, ...args: A) => (obj: T) => ReturnType<T[K]>

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

throttle(fn: () => void, ms: number, leading = true) => () => void

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

TypeScript

This module uses TypeScript and publishes type definitions on NPM.

License

Apache 2.0