This is a chess implementation in javascript and a fork of
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3.2 KiB

JavaScript Chess

This program is a JavaScript implementation of the board game Chess, with a computer player opponent. All move types are supported, including en passant, castling and promotion.

Try it out here. Usage is shown below the chessboard. At least Internet Explorer (8 or later), Chrome and Firefox should work.

Code Structure

Source files are placed in the src directory. Minification and linting files are placed in the build directory. Source file contents:

  • chess.js: Constants, utilities and the Chess namespace.
  • bitboard.js: 64-bit bit twiddling tools.
  • zobrist.js: Game state hash calculator. Currently only used for the threefold repetition rule, but will be used in the transposition table implementation.
  • move.js: Piece movement representation.
  • position.js: Chess game state and mutation.
  • parser.js: Parser for various Chess notations.
  • ai.js: Artificial intelligence, i.e. computer opponent. Basic alpha-beta pruned minimax with a simple evaluation function.
  • ui.js: User interface code.
  • chess.include.js: Includes all of the above files.
  • chess.css: User interface style.
  • chess.ico: Icon.
  • chess.html: Main game file.
  • test.js: Automated tests.
  • test.html: Automated test runner.


To compile the minified version using in the build directory, you need bash and the Closure compiler. You may need to adjust the .jar location in Compiled files are placed in the top-level directory.

To lint using in the build directory, you need bash and JavaScript Lint. You may need to adjust lint's path in

To run the tests, open test.html in the src directory.


  • Static exchange evaluation
  • Transposition table
  • Iterative deepening
  • Negamax formulation
  • AI randomness
  • Take game phase into account in evaluation
  • Take mobility into account in evaluation
  • Killer heuristic
  • Late-check castling legality
  • Tie-detection
  • Move pieces without drag and drop
  • Underpromotion
  • Show captured pieces in the UI
  • Don't hardcode board target div to UI
  • UI for loading game state from parsable Chess notation(s)
  • More tests


The Chess implementation is distributed under the MIT license. See accompanying LICENSE file for details.

Third-party components are distributed/used under their respective license:

  • jQuery: MIT (used via jQuery CDN)
  • jQuery UI: MIT (used via jQuery CDN)
  • jQuery UI Touch Punch: MIT (used via CloudFlare CDN)
  • Augment.js: MIT (used via CloudFlare CDN)
  • QUnit: MIT (used via jQuery CDN)
  • The jQuery extern file in the build directory: Apache 2