SystemJS is a dynamic dependency manager and universal module loader that resolves and executes JavaScript modules across different browser and server environments. It functions as an import map polyfill, mapping bare module specifiers to absolute URLs to manage dependencies without requiring a build step.
The project provides a system for integrating diverse formats, including AMD and global scripts, into a modern ES module workflow. It enables browser module polyfilling for environments that lack native support for ES modules and import maps, and it allows for dynamic runtime hot-reloading by managing the module registry.
Its capabilities cover custom asset loading for non-JavaScript files such as WebAssembly, CSS, and JSON. The loader also supports modular dependency management, the execution of modules in Node.js, and the ability to verify module integrity using cryptographic hashes.