Fromable

Fromable allows you take any iterable, tranform it using .map and .filter, and then output it into a collection, without creating intermediate values.

Motivation

arr.filter(isSomething).map(transform); will allocate two new arrays into memory, when you only want one. Each time you run .filter or .map, you're creating a whole new array, which will need to be garbage collected.

Additionally, it only operates on arrays. filtering/mapping on Sets/Maps/strings is not yet possible.

Install

npm i fromable

Usage

from will accept any Iterable (array, string, Set, Map, etc).

into will accept a number, string, array, Set, Map, or object. It accepts an optional second argument, which will handle custom combinations.

import { from } from 'fromable'; // 😆

// chain map and filter on arrays
from([1,2,3,4,5,6])
    .map(val => val + 2)
    .filter(val => val % 2 === 0)
    .map(val => val ** 2)
    .into([]) //=> [16, 36, 64]

// accumulate into a number
from(new Set([1,2,3,4,5,6]))
    .map(val => val + 2)
    .filter(val => val > 4)
    .into(0) //=> 18

// add entries to an object
from("abc")
    .map((val, idx) => [v, i])
    .into({}) //=> { a: 1, b: 2, c: 3}

// zip together multiple iterables
from([1, 2, 3], [4, 5, 6], [7, 8, 9]) 
    .map(([first, second, third]) => first + second + third)
    .into([]) //=> [12, 15, 18]

// use custom combiner
from([1,2,3,4])
    .into(new Queue(), (queue, curr) => queue.enqueue(curr)) //=> Queue <1, 2, 3, 4>