Flexily

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Contributing to Flexily ​

Thanks for your interest in contributing to Flexily! This guide covers the essentials.

Prerequisites ​

  • Bun >= 1.0 (runtime and package manager)
  • Node.js >= 23.6 for development (native TS type-stripping); the published package supports Node >= 18
  • TypeScript >= 5.7

Getting Started ​

bash
git clone https://github.com/beorn/flexily.git
cd flexily
bun install
bun run build       # Compile TypeScript
bun run typecheck   # Type check without emitting

Running Tests ​

bash
bun test                    # All tests (1774)
bun test tests/layout.test.ts   # Specific test file
bun test --watch            # Watch mode

The most important test layer is the re-layout consistency suite (1200+ fuzz tests). Always run it after layout changes:

bash
bun test tests/relayout-consistency.test.ts

Running Benchmarks ​

Performance is Flexily's core value proposition. Any change touching hot paths (src/layout-zero.ts, src/node-zero.ts) must include benchmark verification.

bash
# 1. Check for CPU-heavy processes that would skew results
top -l 1 -n 5 -stats command,cpu | head -10

# 2. Capture baseline BEFORE changes
bun bench bench/yoga-compare-warmup.bench.ts > /tmp/bench-before.txt

# 3. Make your changes...

# 4. Re-check CPU load (must match pre-change conditions)
top -l 1 -n 5 -stats command,cpu | head -10

# 5. Capture AFTER changes
bun bench bench/yoga-compare-warmup.bench.ts > /tmp/bench-after.txt

# 6. Compare
diff /tmp/bench-before.txt /tmp/bench-after.txt

Acceptable performance impact: < 5% regression for minor features; no regression for refactoring.

Code Structure ​

src/
├── index.ts        # Main export
├── node-zero.ts    # Node class with FlexInfo (hot path)
├── layout-zero.ts  # Layout algorithm (~2700 lines, hot path)
├── constants.ts    # Flexbox constants (Yoga-compatible)
├── types.ts        # TypeScript interfaces
├── utils.ts        # Shared utilities
└── classic/        # Allocating algorithm (for debugging)

See docs/ for detailed documentation on the algorithm, API, performance, and testing methodology.

Pull Request Guidelines ​

  1. Run the full test suite (bun test) — all 1774 tests must pass
  2. Run bun run typecheck — no type errors
  3. Benchmark if touching hot paths — include before/after numbers in the PR description
  4. Keep Yoga API compatibility — don't break the public API surface
  5. Don't allocate in hot paths — layout-zero.ts avoids new in layout loops by design
  6. Don't add WASM — pure JavaScript is the point

Architecture Principles ​

  • Zero-allocation design in the layout engine — reuses FlexInfo objects
  • Yoga API compatibility — same constants, same method names
  • Two algorithms: zero (production, zero-alloc) and classic (debugging, allocating)

For the full development workflow and detailed guidance, see CLAUDE.md.

License ​

By contributing, you agree that your contributions will be licensed under the MIT License.

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