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 supplied to it.

identity(42); //=> 42

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

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

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<T>(fn: (...args: T) => void, ms: number, { leading, trailing, debounce }) => (...args: T) => 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

spread<T, R>(fn: (...args: T) => R) => (args: T) => R

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

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

flip<T1, T2, R>(fn: (arg1: T1, arg2: T2) => R) => (arg2: T2, arg1: T1) => R

Flip a binary fn argument order.

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

partial<T, U, R>(fn: (...args1: T, ...args2: U) => R) => (...args: U) => R

Returns a partially applied fn with the supplied arguments.

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

sequence<T>(...fns: Array<(input: T) => T>) => (input: T) => T

Left-to-right function composition.

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

compose<T>(...fns: Array<(input: T) => T>) => (input: T) => T

Right-to-left function composition.

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

nary<T, R>(n: number, fn: (...args: T) => R) => (...args: T) => R

Fix the number of receivable arguments in origFn to n.

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

TypeScript

This module uses TypeScript and publishes type definitions on NPM.

License

Apache 2.0