What Are CJS, AMD, UMD, ESM, System, and IIFE?

Module formats illustrated with Rollup examples

Photo by Farzad Nazifi on Unsplash.

Modern JavaScript projects need a bundler to compile small pieces of code into something larger and more complex, such as a library or application. The popular bundlers are webpack, Rollup, Parcel, RequireJS, and Browserify. They transform JavaScript code into modules that can be loaded as one bundle.