@coddist/mmap v1.0.0

MMAP

Nothing fancy and complicated, just a mutable map function that maps array items in place.

Usage

Install:

# with Yarn
yarn add @coddist/mmap

# with NPM
npm install @coddist/mmap

Enjoy:

import mmap from '@coddist/mmap';

const array = [1.324, 34.1234, 42.346828];
const result = mmap(array, Math.floor); // [1, 34, 42]
result === array; // true

Motivation

Works tiny bit faster than native Array.prototype.map due to the fact it maps in place without creating new instances. And well, sometimes that's just what we need.

API

Mutates array provided as the first argument, modifying each item to the result of calling function, the second argument, on this item.

mmap(array, cb, cbCtx);

CallbackFn is called passing following arguments:

• item: the current element of the array
• index: the index of the item
• array: actual array mmap is called upon

Return value

Returns the same array mmap was called upon

TypeScript usage

By default, TypeScript will expect return value of provided function to be of the same time as array element. This will fail:

const array = [1, 2, 3];
const cb = (n) => String(n);

mmap(array, cb); // TS Error: Type 'string' is not assignable to type 'number'

Generally, it's not advised to use this function with callbacks returning different type, but if you 100% know what you're doing you can provide input and output generic types like so:

const array = [1, 2, 3];
const cb = (n) => String(n);

const result = mmap<number[], string[]>(array, cb);
/**
 * Same as doing:
 * `const result = array as unknown as string[]`
 */

NOTE that TS will still treat array as number[] which it no longer will be, so using native map method would be wiser in this case.