There's a bunch of maps or polyfills you can use to communicate with external features. Things like WebGL for example. So it just maps those calls to whatever f

There's a bunch of maps or polyfills you can use to communicate with external features. Things like WebGL for example. So it just maps those calls to whatever functions you can provide. Or if your C code uses the file system, you can either pick a virtual file system (for web code) or a real file system (for node applications). The opposite is also true - you have a html5.h header file you can reference to do DOM/browser manipulations from your native code. It's pretty fascinating.