If you specify an HTML file extension (for example, -o with-glue.html) for the output, you'll end up with a with-glue.html, with-glue.js, and with-glue.wasm file (assuming you also specified -s WASM=1). If you have a main() function in the source C/C++ file, it'll execute that function as soon as the HTML loads. Let's compile our example C code to see this in action. To compile it with the HTML file and JavaScript glue code, cd into the /chapter-05-create-load-module folder and run the following command:

emcc with-glue.c -O3 -s WASM=1 -s USE_SDL=2 -o with-glue.html

The first time you run this command, Emscripten is going to download and build the SDL2 library. It could take several minutes to complete this, but you'll only need to wait once. Emscripten caches the library so subsequent builds will be much faster. Once the build is complete, you'll see three new files in the folder: HTML, JavaScript, and Wasm files. Run the following command to serve the file locally:

serve -l 8080

If you open your browser up to http://127.0.0.1:8080/with-glue.html, you should see the following:

The blue rectangle should be moving diagonally from the upper-left corner of the red rectangle to the lower-right. Since you specified a main() function in the C file, Emscripten knows it should execute it right away. If you open up the with-glue.html file in VS code and scroll to the bottom of the file, you will see the loading code. You won't see any references to the WebAssembly object; that's being handled in the JavaScript glue code file.