Arpad: ELO Rating System for Node.js

This is an implementation of ELO for Node.js (ELO is named after Arpad Elo, hence the package name). This module is heavily tested and has many features used in real-world ELO situations.

Installation

$ npm install arpad

Simple Usage

This is a fairly simple example showing the most common usage for Arpad:

const Elo = require('arpad');

const elo = new Elo();

let alice = 1_600;
let bob = 1_300;

let new_alice = elo.newRatingIfWon(alice, bob);
console.log("Alice's new rating if she won:", new_alice); // 1,605

let new_bob = elo.newRatingIfWon(bob, alice);
console.log("Bob's new rating if he won:", new_bob); // 1,327

Complex Usage

This is a more complex example, making use of K-factor tables and score values:

const Elo = require('arpad');

const uscf = {
  default: 32,
  2100: 24,
  2400: 16
};

const min_score = 100;
const max_score = 10_000;

const elo = new Elo(uscf, min_score, max_score);

let alice = 2_090;
let bob = 2_700;

let odds_alice_wins = elo.expectedScore(alice, bob);
console.log("The odds of Alice winning are about:", odds_alice_wins); // 0.029
alice = elo.newRating(odds_alice_wins, 1.0, alice);
console.log("Alice's new rating after she won:", alice); // 2121

odds_alice_wins = elo.expectedScore(alice, bob);
console.log("The odds of Alice winning again are about:", odds_alice_wins); // 0.034
alice = elo.newRating(odds_alice_wins, 1.0, alice);
console.log("Alice's new rating if she won again:", alice); // 2144

Running Tests

If you'd like to contribute be sure to run npm install to get the required packages and then make changes. Afterwards simply run the tests. If everything passes your Pull Request should be ready.

$ npm test

License

MIT