HaxElo.js

A simple library to calculate Elo rating changes for teams and individual players. Initially made for Haxball, but can be used in any sort of Elo rating system.

Installation

To install HaxElo.js, you can use npm:

npm install haxelo

Usage

Node.js To use the library in a Node.js project, require it as follows:

const HaxElo = require('haxelo');

// Team Elo Change Example
const red = [1200, 1300, 1400]; // Elo ratings for the red team
const blue = [1100, 1000, 900]; // Elo ratings for the blue team
const score = 1; // Red wins
const factor = 32; // K factor

const result = HaxElo.teamEloChange(red, blue, score, factor);
console.log(result); // Output: { redChange: 13, blueChange: -13 }

// Player Elo Change Example
const red = 1500;
const blue = 1400;
const score = 1; // red wins
const factor = 32; // K factor

const result = HaxElo.playerEloChange(playerA, playerB, score, factor);
console.log(result); // Output: { redChange: 10, blueChange: -10 }

If you want to add it in the web you can just copy the following code:

const HaxElo = (() => {
    function teamEloChange(red, blue, score, factor) {
        if (red.length !== blue.length) throw new Error("Both teams must have the same size.");
        var w = red.reduce((a, x) => x + a, 0) / red.length;
        var l = blue.reduce((a, x) => x + a, 0) / blue.length;
        var E_w = 1 / (1 + Math.pow(10, (l - w) / 400));
        var E_l = 1 / (1 + Math.pow(10, (w - l) / 400));
        var S_w, S_l;
        if (score == 1) {
            S_w = 1;
            S_l = 0;
        }
        else if (score == 2) {
            S_w = 0;
            S_l = 1;
        }
        else if (score == 0) {
            S_w = 0.5;
            S_l = 0.5;
        }
        else {
            throw new Error("Score must be 0, 1 or 2.");
        }
        var result = { redChange: Math.round(factor * (S_w - E_w)), blueChange: Math.round(factor * (S_l - E_l)) };
        return result;
    }

    function playerEloChange(red, blue, score, factor) {
        var E_a = 1 / (1 + Math.pow(10, (blue - red) / 400));
        var E_b = 1 / (1 + Math.pow(10, (red - blue) / 400));
        var S_a, S_b;
        if (score === 1) {
            S_a = 1;
            S_b = 0;
        }
        else if (score === 2) {
            S_a = 0;
            S_b = 1;
        }
        else {
            S_a = 0.5;
            S_b = 0.5;
        }
        var result = { redChange: Math.round(factor * (S_a - E_a)), blueChange: Math.round(factor * (S_b - E_b)) };
        return result;
    }

    return {
        teamEloChange: teamEloChange,
        playerEloChange: playerEloChange
    };
})();

Contributions

Contributions to haxelo are welcome! Feel free to fork this repository, make changes, and submit pull requests to enhance its functionality or improve its documentation.