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CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Commands

npm run build          # Compile TypeScript to dist/
npm test               # Run tests (mocha dist/timecode.test.js)
npm run test-coverage  # Run tests with nyc coverage reporting

Tests run against compiled output in dist/, so always run npm run build before npm test when source changes.

There is no separate lint script — ESLint is configured but not wired into a script.

Architecture

This is a single-class TypeScript library (src/timecode.ts) with no runtime dependencies. The Timecode class is the entire public API. Tests live in src/timecode.test.ts, colocated with the source, and are compiled alongside it.

Build output goes to dist/ (tracked in source control). The package entry points directly into dist/src/timecode.js and dist/src/timecode.d.ts.

Key design patterns

  • Immutability: arithmetic methods (add, subtract, pulldown, pullup, slowdown, speedup) return new Timecode instances rather than mutating.
  • Setter chaining: field setters (setHours, setMinutes, etc.) return this and handle overflow/underflow automatically (e.g., setting 72 minutes wraps to 1 hour 12 minutes).
  • Drop-frame timecode: 29.97 and 59.94 fps use drop-frame (skipping frame numbers 0 and 1 at every minute except every 10th). The separator in toString() changes from : to ; for drop-frame rates.
  • Cross-rate arithmetic: add/subtract handle operands at different frame rates by converting to a common rate before computing.

Constructor inputs (ConvertibleToTimecode)

The constructor accepts: another Timecode, a timecode string (HH:MM:SS:FF or HH:MM:SS.mmm), a plain object with TimecodeAttributes fields, a frame count as a number, or a Date object.

Frame rate conversions

  • pulldown(rate) / pullup() — preserves real-time position while changing frame rate (e.g., 24→29.97)
  • slowdown(rate) / speedup() — changes playback speed without preserving real time

Style

Follows the Airbnb JavaScript Style Guide, enforced with ESLint (flat config, eslint.config.mjs). Max line length is 140 characters. TypeScript strict mode is enabled.

Testing notes

Test values are verified against Avid Media Composer's timecode calculator. Tests aim for 100% coverage.