Mozilla PDF.js is a comprehensive, web-standards-based PDF rendering library and viewer built entirely in JavaScript. It parses and renders PDF documents in the browser using HTML5 Canvas and SVG, with a worker thread for heavy parsing to keep the UI responsive. The library supports PDF versions 1.0 through 2.0, including encryption, digital signatures, XFA forms, Acrobat JavaScript scripting, and a full annotation editing suite (free text, ink, highlight, stamp, signature). It also provides a complete web viewer application with sidebar, find bar, presentation mode, and printing, plus a Chrome extension and Firefox integration. The architecture is modular: a core worker thread handles parsing, font rendering, and image decoding (using WebAssembly for JPEG2000, JBIG2, Brotli, and ICC color management), while the display layer manages canvas rendering, text extraction, and annotation overlays. The viewer layer provides UI components with an event bus for decoupled communication. The codebase demonstrates exceptional craftsmanship with clean abstractions (factory patterns, base classes, lazy initialization), extensive unit and integration tests, and a sophisticated build system that targets generic web, legacy browsers, Chrome, and Firefox. Key reusable patterns include a PostScript-to-typed-array compiler with fallback interpreter, a TrueType glyf table parser/writer, an operator list optimizer using state machines, a generic message handler for worker communication, and image processing utilities for signature extraction. The project is actively maintained with frequent commits, low technical drift, and a large community.
SingleFileZ is a browser extension (Chrome/Firefox/Edge) and CLI tool that saves complete web pages as self-extracting HTML/ZIP polyglot files. The core output format embeds a ZIP archive containing all page resources (HTML, CSS, images, fonts, frames) inside an HTML wrapper with a JavaScript bootstrap that extracts and displays the page without external dependencies. The extension offers extensive configuration including multiple profiles, URL-based auto-save rules, cloud uploads (Google Drive, Dropbox, GitHub, WebDAV), an annotation editor for notes/highlights/cut operations, batch saving, and file name templating. Architecturally, the project is a multi-browser extension with background scripts orchestrating page capture, content scripts handling in-page UI and resource collection, and a task queue for managing parallel saves. It relies heavily on message passing between contexts and includes custom infrastructure: a binary serialization format (YABSON) for efficient data transfer, a full ZIP read/write library with support for encryption and streaming, and a fork of Mozilla's Readability.js for article extraction. The CLI component uses Docker to run headlessly, delegating to the `single-filez-cli` npm package. The codebase is large and feature-rich but shows signs of maintainability strain: core modules are distributed as minified build artifacts in `lib/`, the README states SingleFileZ has been merged into its parent project SingleFile (suggesting this repo is superseded), and it relies on Manifest v2 which is being phased out by browsers. The custom polyfills and browser-specific workarounds add complexity. Despite this, several components (YABSON serialization, the ZIP library, cloud upload abstractions) are well-isolated and could be reused independently with minimal modification.