Delo

Delo is a TypeScript implementation of the Elo rating system for the Deno runtime.

Usage

import {
  Period,
  Player,
  Outcome,
} from "https://deno.land/x/delo@v0.1.0/mod.ts";

const players: { [key: string]: Player } = {
  Alice: new Player(1915),
  Bob: new Player(1453),
  Charlie: new Player(1375),
  Doug: new Player(1991),
  Earl: new Player(),
};

const period = new Period();

period.addGame(players.Alice, players.Bob, Outcome.LOSS);
period.addGame(players.Doug, players.Charlie, Outcome.DRAW);
period.addGame(players.Earl, players.Bob, Outcome.WIN);
period.addGame(players.Charlie, players.Alice, Outcome.WIN);
period.addGame(players.Doug, players.Earl, Outcome.LOSS);

period.calculate();

for (const name in players) {
  console.log(`${name}: ${players[name].rating.toFixed(0)}`);
}

Expected Output

Alice: 1870
Bob: 1465
Charlie: 1409
Doug: 1957
Earl: 1533

API

Outcome

Outcome provides three constants to represent possible game results.

• WIN - 1
• DRAW - 0.5
• LOSS - 0

Player

Properties

• id: string
  • A unique identifier for the Player object (UUID v4 by default).
• rating: number
  • The Player's Elo rating.

Instantiation

A new Player has a default rating of 1500.

new Player();

Pass a positive number for a different initial rating.

new Player(1800);

Additionally pass a string to uniquely identify the player. By default, a v4 UUID is generated internally to keep track of players. You may want to pass an ID if, for example, you already maintain a database of players keyed by unique IDs.

new Player(1924, "jimmy23");

Period

Properties

• length: number
  • The number of games played during the period.

Methods

• addGame(player1: Player, player2: Player, score: Outcome)
  • Adds a game between player1 and player2, with score representing whether player1 won, drew, or lost against player2.
• reset()
  • Clears all games from the period. Does not affect player ratings.
• calculate()
  • Updates the rating of all players who played games during this period.

Instantiation

New periods have a default K-factor of 24. The K-factor represents the maximum possible rating adjustment per game.

new Period();

Pass a positive number to adjust the K-factor.

new Period(40);