As a Computer Science Engineer and a Chess enthusiast, I’ve always been fascinated by how digital chess boards work. We take it for granted when we drag a piece on Chess.com or Lichess, but under the hood, there is a complex orchestration of State Management, DOM Manipulation, and Coordinate Geometry.
Recently, I built my own PGN Parser & Visualizer for this blog. I didn't want a static board; I wanted "butter-smooth" animations where pieces lift, slide, and land naturally.
Here is a deep dive into the technology and algorithms behind my Chess Parser.
1. The Brain: Chess.js & State Management
Building a chess engine from scratch involves writing thousands of lines of code just to validate moves (en passant, castling rights, promotion, checks). Instead of reinventing the wheel, I used Chess.js.
Chess.js acts as the "Referee". It doesn't handle the UI (the board you see); it handles the Logic (the rules).
// Load a game from a FEN String
chess.load("rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1");
// Make a move
const move = chess.move("Nf6"); // Returns move object or null
2. The DNA of a Position: FEN Strings
To render the board, we need to know where every piece is. In the chess world, we use FEN (Forsyth–Edwards Notation). It is a string that compresses the entire state of the board.
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
- Rows: Separated by
/.rnbqkbnrmeans Black's back rank. - Numbers:
8means "8 empty squares". - Turn:
wmeans White to move.
My parser reads this string, loops through the 64 squares, and decides whether to place a <div> with a piece image or leave it empty.
3. The "Butter Smooth" Animation Logic 🧈
This was the hardest part. How do you animate a piece moving from e2 to e4?
If I simply update the DOM, the piece "teleports". To achieve the Lift + Slide + Land effect, I wrote a custom animation algorithm using the FLIP (First, Last, Invert, Play) concept.
Step A: Calculate Coordinates
I use getBoundingClientRect() to find the exact pixel coordinates of the Source Square (Start) and Destination Square (End).
const dstRect = destSquare.getBoundingClientRect();
const deltaX = dstRect.left - srcRect.left;
const deltaY = dstRect.top - srcRect.top;
Step B: The Ghost Element
I create a "Ghost" piece (a clone of the original) and append it to the <body> with position: fixed. This allows it to float above everything else, independent of the board's grid layout.
Step C: CSS Transitions
I use JavaScript Promises to orchestrate the CSS transitions in 3 phases:
- Lift: Scale up the piece (1.15x) to simulate picking it up.
- Slide: Translate (Move) the piece using
transform: translate(deltaX, deltaY). - Land: Scale back down to 1.0 and fade out.
ghost.style.transform = `translate(${deltaX}px, ${deltaY}px) scale(1.15)`;
ghost.style.transition = "transform 0.4s cubic-bezier(0.4, 0, 0.2, 1)";
4. Handling PGN (Portable Game Notation)
The tool allows users to paste a PGN (e.g., "1. e4 e5 2. Nf3..."). Parsing text is tricky because PGNs often contain comments, recursive variations, or different header formats.
I implemented a Regex Cleaning step to strip out metadata ([Event "..."]) and focus purely on the move text, which is then fed into the Chess.js engine to generate the move history queue.
Conclusion
Building this project bridged the gap between my Engineering degree and my hobby. It taught me that Data Structures (Arrays vs Maps for board representation) and Algorithms (Backtracking for legal move generation) are not just theory—they build the tools we use every day.
Feel free to try out the tool on the homepage and let me know if you find any bugs!
Try the Chess Parser Live
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