Google Closure Compiler vs Parcel

Google Closure Compiler optimizes JavaScript by analyzing code, removing dead code, and rewriting and minimizing what remains. It can also check syntax, references, and types, and warn about illegal JavaScript, risky operations, and common pitfalls. Google says smaller output files can help applications load faster and reduce bandwidth needs. Compilation options include WHITESPACE_ONLY, SIMPLE, and ADVANCED; the repository README also lists BUNDLE. ADVANCED applies aggressive transformations and symbol renaming to improve compression, so preserving program behavior requires care. The project is available as a command-line Java application, a library used through Bazel, and an NPM package. Released JARs are distributed through Maven. The repository documents Maven, NPM, Bazel, command-line Java, and a NodeJS API. Building the compiler requires Java 21 or later, NodeJS, Git, and Bazelisk. Its input restrictions include use of goog.module() and goog.require(), and ES6 import/export support is not actively maintained. The NPM packages are built and distributed by an open source contributor, not Google. The compiler is free.

Parcel is a free, open source, zero-configuration build tool for web projects. It handles HTML, CSS, JavaScript, TypeScript, JSX, Flow, images, fonts, videos, Sass, SVG, Vue, Node, Electron, GraphQL, MDX, XML and other file types out of the box. It can automatically install plugins and development dependencies for additional file types. For development, Parcel includes an HTTPS server with an API proxy and automatically updates code in the browser, with React Fast Refresh and Vue hot-reloading integrations. Terminal and browser diagnostics include syntax-highlighted code frames, hints and documentation links. Production features include tree shaking, minification, image optimization, code splitting, content hashing, and Gzip and Brotli compression. Builds use worker threads and caching, with lazy development builds also supported. Parcel can target declared browser environments, handle workers, build libraries for multiple targets and build monorepos with one command. A plugin system and programmatic API support customization and integration into existing build systems. Its development server builds only one target at a time and defaults to a modern browser target; compression is not enabled by default.