@ironarachne/rng

A comprehensive random number generation library for TypeScript and JavaScript. It provides a seeded random number generator (RNG) class for deterministic results, along with a set of global convenience functions for quick and easy use.

Note that this is not meant for cryptography and should not be considered "safe" for such purposes.

Documentation available at: ironarachne.github.io/rng

Installation

npm install @ironarachne/rng
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Usage

The RNG Class

The core of this library is the RNG class. You can instantiate it with a seed (number or string) to get a deterministic sequence of random numbers. This is ideal for procedural generation, games, or testing where reproducibility is key.

import { RNG } from '@ironarachne/rng';

// Initialize with a numeric seed
const rng1 = new RNG(12345);
console.log(rng1.int(1, 100)); // Always produces the same sequence for seed 12345

// Initialize with a string seed
const rng2 = new RNG("my-seed-string");
console.log(rng2.item(['apple', 'banana', 'cherry']));
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Methods

• next(): Returns a random float between 0 (inclusive) and 1 (exclusive).
• int(min, max): Returns a random integer between min and max (inclusive).
• float(min, max): Returns a random float between min and max.
• bellFloat(min, max): Returns a random float between min and max with a bell-curve distribution (approximated by summing 3 random floats).
• item(array): Returns a random item from the given array.
• randomSet(count, array): Returns a new array containing count unique items selected randomly from the source array. The source array is not modified. Throws an error if count exceeds the source array's length.
• randomString(length): Generates a random alphanumeric string of the specified length.
• shuffle(array): Shuffles the given array in place using the Fisher-Yates algorithm.
• simple(max): Returns a random float between 1 and max.
• weighted(items): Selects a value from an array of WeightedEntry objects. Each entry must have a value and a commonality (weight). Weights must be non-negative finite numbers; an entry with a weight of 0 is never selected, and fractional weights are supported. Returns the value of the selected entry. Throws an error if the list is empty, a weight is negative, NaN, or infinite, or the total weight is zero.

const lootTable = [
  { value: 'gold', commonality: 10 },
  { value: 'silver', commonality: 50 },
  { value: 'copper', commonality: 100 }
];
const loot = rng.weighted(lootTable); // Returns 'gold', 'silver', or 'copper'
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Global Convenience Functions

For simple use cases where you don't need to manage a specific seed instance, the library exports a global instance and wrapper functions. These share a single global state.

import { int, item, setSeed } from '@ironarachne/rng';

// Optional: Set the global seed
setSeed(Date.now());

const roll = int(1, 20);
const fruit = item(['apple', 'banana', 'cherry']);
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Available global functions:

• bellFloat(min, max)
• float(min, max)
• int(min, max)
• item(array)
• randomSet(count, array)
• randomString(length)
• setSeed(seed)
• shuffle(array)
• simple(max) (Returns 1 to max)
• weighted(items)

Development

Setup

Node 20 or newer is required.

git clone https://github.com/ironarachne/rng.git
cd rng
npm install
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Commands

Command	What it does
npm run check	Lint, build, and test — run this before pushing.
npm test	Run the Vitest suite.
npm run lint	Check formatting and lint rules with Biome.
npm run lint:fix	Apply formatting and safe lint fixes.
npm run build	Compile TypeScript to dist/.
npm run docs	Generate the TypeDoc site into docs/.

dist/ and docs/ are generated output and are not committed.

Contributing

Contributions are welcome. See CONTRIBUTING.md for the pull request process and CODE_STYLE.md for the conventions this codebase follows.

In short: branch from main, run npm run check, and open a pull request. main is protected, so every change lands through review with CI green.

License

MIT — see LICENSE.