Rollup is a production-grade JavaScript module bundler that compiles small code fragments into optimized single-file or multi-chunk outputs. It is used extensively in the JavaScript ecosystem (e.g., by Vite, React, and many libraries) to produce distributable packages in formats such as ES modules, CommonJS, AMD, UMD, IIFE, and SystemJS. The core functionality includes static analysis for tree-shaking, dependency resolution, chunking with manual and dynamic splits, source map generation, and a comprehensive plugin system for customization. The architecture is centered around a graph-based module resolution pipeline. Input files are parsed into an AST (using a Rust-based parser via NAPI or WASM for performance), then analyzed for imports, exports, and side effects. The tree-shaking engine traces variable usage and eliminates dead code. Modules are grouped into chunks based on entry points, manual chunk definitions, and dynamic imports, then rendered by format-specific finalisers. The plugin system provides hooks at every stage (resolution, loading, transformation, output generation) and supports both sequential and parallel execution. Key entry points include the CLI (`cli/cli.ts`), the programmatic API (`src/node-entry.ts`), and the core `rollup` function (`src/rollup/rollup.ts`). The data flow begins with configuration loading (from CLI flags or config files), followed by module resolution, AST parsing, tree-shaking analysis, chunk assignment, and final output generation. The watch mode (`src/watch/watch.ts`) re-triggers the pipeline on file changes. External dependencies include various `@rollup/plugin-*` packages for common tasks (e.g., resolving node modules, transforming TypeScript), `source-map` for source map handling, `fsevents` for file watching on macOS, and the Rust `swc_ecma_ast` crate for fast parsing. The project maintains native binaries for 25+ platforms and a WASM variant for browser environments.
SortYourMusic is a client-side web application that lets users sort their Spotify playlists by musical attributes like tempo, energy, danceability, loudness, valence, and more. It uses the Spotify Web API with PKCE OAuth for authentication and runs entirely in the browser with no backend server. The repository contains two versions: an older monolithic implementation (web/) using jQuery, Bootstrap 3, and Underscore.js, and a modern modular rewrite (web2/) using vanilla ES modules, CSS custom properties, and no framework dependencies. The modern version demonstrates clean architecture with separate modules for authentication, API calls, state management, views, and utility functions. Key features include BPM filtering with doubled BPM support, artist separation ordering, and the ability to save sorted playlists as new copies or overwrite existing ones.