Fromable allows you take any iterable, tranform it using .map and .filter, and then output it into a collection, without creating intermediate values.
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.
npm i fromable
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, i) => [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>