v4.0.2

Changed

• updated description to mention initial rating calculation
• removed misleading keywords (matchmaking, pvp, rank)
• added performance-rating and initial-rating keywords

v4.0.1

Fixed

• documented delta, expected, and kFactor functions
• documented all exported types (GameOptions, GameType, KFactorOptions,
  PlayerOptions, Result, ResultAndOpponent)
• documented PlayerOptions.k override field
• removed broken CONTRIBUTING.md link

v4.0.0

Changed

• BREAKING: expected() now uses the official FIDE §8.1.2 discrete lookup
  table instead of the continuous formula. Return values are now discrete (0.50,
  0.51, ..., 1.00) matching FIDE exactly. For rating differences > 735 (only
  possible via the 2650+ cap exemption), the continuous formula is used as a
  fallback.

Added

• Source comment in kFactor() citing FIDE Rapid & Blitz regulations for K=20.
• Integration test confirming the 2650+ cap exemption propagates correctly
  through update().

v3.1.0

Fixed

• expected(): players rated 2650 or above are no longer subject to the
  400-point rating difference cap, per FIDE §8.3.1 (effective 1 October 2025).
• update(): rating changes of exactly ±0.5 now round away from zero (e.g. −0.5
  → −1), as required by FIDE §8.3.4.

v3.0.0

Added

• gamesInPeriod option in KFactorOptions and PlayerOptions — when
  provided, applies the FIDE §8.3.3 K-factor cap: if K × n > 700, K is reduced
  to Math.floor(700 / n). Throws RangeError if gamesInPeriod is not a
  positive integer.

Changed

• kFactor() return type widened from 10 | 20 | 40 to number to accommodate
  capped values.

v2.3.0

Added

• initial(games: ResultAndOpponent[]) function implementing FIDE §8.2 initial
  rating calculation for unrated players. Injects two hypothetical 1800-rated
  draws per the spec, caps result at 2200, and reuses the existing
  ResultAndOpponent type.

v2.2.1

Changed

• Updated README with friendlier intro, quick start section, annotated usage
  examples, and FIDE compliance selling points

v2.2.0

Changed

• KFactorOptions and PlayerOptions: games field renamed to gamesPlayed
  for clarity

Migration

// Before
kFactor({ games: 5, rating: 1400 });
update({ games: 30, rating: 1400 }, 1600, 1);

// After
kFactor({ gamesPlayed: 5, rating: 1400 });
update({ gamesPlayed: 30, rating: 1400 }, 1600, 1);

v2.1.0

Added

• GameType type ('blitz' | 'rapid' | 'standard') exported from the package

Changed

• KFactorOptions and GameOptions now use gameType?: GameType instead of
  the mutually exclusive isBlitz?: boolean / isRapid?: boolean pair

Removed

• isBlitz and isRapid fields removed from KFactorOptions and
  GameOptions; use gameType: 'blitz' or gameType: 'rapid' instead

Migration

Replace isBlitz: true with gameType: 'blitz' and isRapid: true with
gameType: 'rapid' everywhere. The field appears in both kFactor options and
the GameOptions third argument of update.

// Before
kFactor({ isBlitz: true, rating: 1400 });
kFactor({ isRapid: true, rating: 2400 });
update(1400, 1600, { isBlitz: true, result: 1 });
update(1400, 1600, { isRapid: true, result: 1 });

// After
kFactor({ gameType: 'blitz', rating: 1400 });
kFactor({ gameType: 'rapid', rating: 2400 });
update(1400, 1600, { gameType: 'blitz', result: 1 });
update(1400, 1600, { gameType: 'rapid', result: 1 });

Player options are unaffected — they still go on the player arguments:

update({ age: 17, rating: 1400 }, 1600, { gameType: 'blitz', result: 1 });

v2.0.0

Changed

• update() now accepts PlayerOptions objects for a and b parameters,
  allowing per-player options (age, games, everHigher2400, k) to be
  passed directly on each player argument
• Game-level options (isBlitz, isRapid, result) are now passed as a
  GameOptions object in the third argument

Removed

• UpdateOptions type removed from public API; use PlayerOptions and
  GameOptions instead
• kA, kB, k (shared) fields removed from third argument; use k on each
  PlayerOptions object instead

Migration

The third argument is now a GameOptions object (or a bare Result shorthand
when no game options are needed). Player-specific options move onto each player
argument as a PlayerOptions object.

// Before — flat options bag
update(1400, 1600, { result: 1 });
update(1400, 1600, { ageA: 17, result: 1 });
update(1400, 1600, { gamesB: 5, result: 1 });
update(1400, 1600, { kA: 40, result: 1 });
update(1400, 1600, { kA: 40, kB: 10, result: 1 });
update(1400, 1600, { isBlitz: true, result: 1 });

// After — per-player objects + game options
update(1400, 1600, 1); // bare result shorthand still works
update({ age: 17, rating: 1400 }, 1600, 1); // age on player A
update(1400, { games: 5, rating: 1600 }, 1); // games on player B
update({ k: 40, rating: 1400 }, 1600, 1); // k on player A
update({ k: 40, rating: 1400 }, { k: 10, rating: 1600 }, 1); // k on each player
update(1400, 1600, { gameType: 'blitz', result: 1 }); // game-level option