Life & fun · December 11, 2024
Lfi – a lazy functional sync, async, and concurrent iteration library
Hey HN! Roughly 4 years ago I started building a lazy functional iteration library for JS/TS. I had a few goals for the library: - Supporting sync, sequential async, and concurrent async iteration - Limiting it to a small number of orthogonal concepts that compose beautifully to solve problems - Making it fully tree-shakeable I built it for myself and have (mostly) been its only user as I refined it. I've used it in lots of personal projects and really enjoyed it. I recently decided it would be nice to spread that enjoyment so I created a documentation website complete with a playground…
Lfi – a lazy functional sync, async, and concurrent iteration library launched on December 11, 2024 with 98 votes, #401 of 5,365 launches that month and more than 90% of that year's launches. The site was still online in September 2026, 1 year on.
In plain words
Lfi is a JavaScript and TypeScript library for lazy functional iteration that handles synchronous, sequential asynchronous, and concurrent asynchronous operations. It emphasizes composable, orthogonal concepts designed to solve iteration problems while maintaining full tree-shakeability for efficient bundling. The library is intended for developers working on personal or professional projects who prefer functional approaches to iteration patterns. It includes documentation and an interactive playground for exploring its capabilities.
written from the facts on this page · September 2026
From the sources
A lazy functional sync, async, and concurrent iteration library for JavaScript and TypeScript
lfi ’s concurrent iterables offer superior performance over p-map , p-filter , and others, because each item flows through the operations independently of other items. import { asConcur , filterConcur , mapConcur , pipe , reduceConcur , toArray } from 'lfi' import pFilter from 'p-filter' import pMap from 'p-map' // Hypothetical delays for each item const mapDelays = [ 5 , 1 , 1 ] const filterDelays = [ 1 , 1 , 5 ] const delay = ms => new Promise ( resolve => setTimeout ( resolve , ms ) ) const mapFn = i => delay ( mapDelays [ i ] * 1000 ) . then ( ( ) => i ) const filterFn = i => delay ( filterDelays [ i ] * 1000 ) . then ( ( ) => true ) // Takes 6 seconds! Each item flows through the //…from lfi.dev
In the maker’s words, at launch
Hey HN! Roughly 4 years ago I started building a lazy functional iteration library for JS/TS. I had a few goals for the library: - Supporting sync, sequential async, and concurrent async iteration - Limiting it to a small number of orthogonal concepts that compose beautifully to solve problems - Making it fully…
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Source: Show HN post ↗ · launch text quoted in part
