Preλude-js

A modular, tree-shaking friendly implementation of Haskell's Prelude library in modern, type-safe JavaScript.

It ships as native ESM, keeps the runtime source in src/ without any legacy top-level compiled output, and is fully compatible with Bun, Node.js, Deno, and modern browsers.

Features

• Curried by Default: Multi-argument functions are curried out of the box to enable elegant function composition and point-free style.
• Native ESM: Fully compatible with native resolution runtimes (explicit .js extensions preserved in imports).
• TypeScript Signatures: Shipped with comprehensive .d.ts declaration files for complete IDE autocomplete and compile-time type safety.
• Tree-Shaking Friendly: Zero external dependencies. Every function lives in its own file, allowing bundlers to strip out unused helpers.

Compatibility

Since prelude-js is implemented as standard ES modules (ESM) with zero external dependencies, it runs seamlessly across all modern JavaScript environments:

• Node.js: >=20.0.0
• Bun: >=1.3.13
• Deno: Full native support (installable via JSR)
• Edge Runtimes: Cloudflare Workers, Vercel Edge Functions, Netlify Edge
• Browsers: Modern browsers natively supporting ESM imports

Installation

bun add preludejs

or

npm install preludejs

Import Styles

You can import either namespace barrels directly from the main entrypoint, or target individual files directly for optimal tree-shaking:

Barrel Imports

import { List, Func, General, Str } from 'preludejs'

List.length([1, 2, 3]) // => 3
Func.const('left', 'right') // => 'left'
Str.capitalize('prelude') // => 'Prelude'

Deep Imports (Optimal Tree-Shaking)

When importing individual functions directly, always preserve the explicit .js extension to comply with native ESM runtime resolution:

import map from 'preludejs/List/map.js'
import compose from 'preludejs/Func/compose.js'

map((x) => x * 2, [1, 2, 3]) // => [2, 4, 6]

Usage Examples

1. Currying & Function Composition

import curry from 'preludejs/Func/curry.js'
import compose from 'preludejs/Func/compose.js'

const add = curry((a, b) => a + b)
const double = (x) => x * 2

// Compose operations right-to-left
const addThenDouble = compose(double, add(2))

addThenDouble(3) // => 10 (double(add(2, 3)))

2. List Operations

import filter from 'preludejs/List/filter.js'
import reduce from 'preludejs/List/reduce.js'

const isEven = (x) => x % 2 === 0
const sum = (acc, x) => acc + x

const evens = filter(isEven, [1, 2, 3, 4]) // => [2, 4]
reduce(sum, 0, evens) // => 6

Layout

• preludejs resolves to src/index.js.
• Barrel modules export namespaces: Func, General, List, Num, Obj, Str.
• Direct imports map directly to the function's runtime module (e.g. preludejs/List/map.js maps to src/List/map.js).

For the complete API reference, see the documentation site.

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