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What is @pdfa-lab/fontkit? ​

Fontkit is an advanced font engine for Node and the browser.

Features ​

  • Supports TrueType (.ttf), OpenType (.otf), WOFF (.woff), WOFF2 (.woff2), TrueType Collection (.ttc), and Datafork TrueType (.dfont) font files.
  • Enables mapping characters to glyphs, including support for ligatures and other advanced substitutions.
  • Reads glyph metrics and lays out glyphs, including support for kerning and other advanced layout features.
  • Handles advanced OpenType features including glyph substitution (GSUB) and positioning (GPOS)
  • Apple Advanced Typography (AAT) glyph substitution features (morx table).
  • Support for getting glyph vector paths and converting them to SVG paths, or rendering them to a graphics context.
  • Supports TrueType (glyf) and PostScript (CFF/CFF2) outlines.
  • Support for color glyphs (e.g. emoji), including Apple’s SBIX table, and Microsoft’s COLR table.
  • Support for AAT variation glyphs, allowing for nearly infinite design control over weight, width, and other axes.
  • Font subsetting support - create a new font including only the specified glyphs.

Improvements in @pdfa-lab/fontkit ​

  • Fully Typed Architecture: Re-engineered from the ground up in native TypeScript, offering robust auto-completion, strict compiler checks, and inline documentation for complex internal font structures (such as layout tables and glyph collections).
  • API documentation; you are currently reading it.
  • Modern ESM Native & CJS Layouts: Shipped with strict, modern dual-package support (.js and .cjs), eliminating old bundler quirks and offering out-of-the-box support for modern frameworks (Vite, Next.js, etc.) alongside backward-compatible UMD browser targets.
  • Modernised Engineering Tooling: Replaced aging, custom hand-crafted build scripts with modern tooling (Rollup/Vite) and an overhauled, modern testing pipeline (Vitest/Jest).

The Typescript Shift ​

The primary limitation of the original codebase and its early forks was the reliance on loose JavaScript objects to represent complex, low-level binary specifications (like OpenType and AAT structures).

By porting @pdfa-lab/fontkit to strict TypeScript, the library has been turned internal structural contracts into a form of static analysis. This migration has eliminated legacy silent bugs, clearly define cross-module internal boundaries (like table registration schemes), and dramatically improve the developer experience for anyone building advanced layout or PDF rendering engines.

History of fontkit ​

The original version of fontkit was written by Devon Govett in JavaScript.

Later, Andrew Dillon created a fork @pdf-lib/fontkit that was mainly focused on improving browser compatibility. It was used by the popular pdf-lib project by the same author. Because pdf-lib has not seen any updates for years, an actively maintained fork @cantoo/pdf-lib has been created.

There is another popular fontkit fork @foliojs-fork/fontkit that included many improvements and bug fixes to the original fontkit.

This version @pdfa-lab/fontkit is based on the original fontkit and the two forks. It tries to incorporate all improvements in the other forks.

The main advantage of @pdfa-lab/fontkit is that the original codebase has been ported to TypeScript, which improves developer experience significantly.

About This Documentation ​

This documentation is a work in progress, and your contributions are highly welcome! If you spot any factual errors, notice missing sections, or have ideas for stylistic improvements, please feel free to open an issue or submit a pull request directly to the pdfa-lab GitHub repository.