TSFish

TSFish is a chess engine with a UCI interface, written with TypeScript and NodeJS, intended for use as a bot on Lichess.org.

2023/09/14 update - TSFish now runs on Bun.

To install bun:

curl -fsSL https://bun.sh/install | bash # for macOS, Linux, and WSL

To run in development mode:

bun start

To build:

bun run build

to run the build:

bun run build:exec

to run tests:

bun test

Implementation Notes

Interface

• UCI - https://backscattering.de/chess/uci/

Multi-threading (src/worker)

• NodeJS supports a form of parallelism with worker_threads, with which you can spawn separate processes to execute code. This isn't traditional multi-threading in the sense that threads can't access the execution context of their parents but worker_threads can communicate to eachother by passing events.

Board representation (src/datatypes)

• Bitboards represented as 64 bit BigInts. Manual enforcement of 64 bit maximum. JavaScript supports bitwise operations which makes it efficient to perform operations such as checking the existence of a piece. Shifting bits on a bitboard is an efficient way to generate moves for a piece.

Game State (src/position)

• The Position class is responsible for game state, board tracking, and move making.

Move generation (src/generator)

• Move generation uses pre-generated move caches but calculates around collisions and captures at runtime.
• Move generation is done in a pseudo-legal manner (doesn't consider checks and pins at generation time) with the exception of castling, in which intermediate steps are "check"ed.
• Pseudo-legal moves are pruned for legality post-generation in the generateMoves() function.

Search (src/search)

• Search uses a simplified Alpha-Beta algorithm (https://www.chessprogramming.org/Alpha-Beta) using the NegaMax framework.

Evaluation (src/search)

• Evaluation uses a symmetric evaluation function in which pieces have weighted scores and the algorithm is essentially score = sum(scores_side) - sum(scores_opposing_side)

PERFT Benchmarks from startpos (approximate, on my dev laptop)

09/17/2023 - optimize around king moves and pinned pieces

• Perft(1) - 0.55 ms
• Perft(2) - 1.4 ms
• Perft(3) - 22 ms
• Perft(4) - 339 ms
• Perft(5) - 10 s

06/15/2023

• Perft(1) - 2.7 ms
• Perft(2) - 13.1 ms
• Perft(3) - 165 ms
• Perft(4) - 2.73 s
• Perft(5) - 63 s (definitely some room for improvement here!)

06/08/2023

• Perft(5) - 141.894s - 155256461 (with invalid moves)
• Perft(4) - 3.144s - 3347643 (with invalid moves)

Improvements TBD

• Magic bitboards to speed up move generation of sliding pieces
• Quiescence search addition to search
• Improved evaluation function
• Support opening books
• Support endgame tablebases