npm vs. RequireJS vs. Browserify

npm is the command-line interface to the npm ecosystem. It is battle-tested, surprisingly flexible, and used by hundreds of thousands of JavaScript developers every day.

RequireJS loads plain JavaScript files as well as more defined modules. It is optimized for in-browser use, including in a Web Worker, but it can be used in other JavaScript environments, like Rhino and Node. It implements the Asynchronous Module API. Using a modular script loader like RequireJS will improve the speed and quality of your code.

Browserify lets you require('modules') in the browser by bundling up all of your dependencies.