We need to compile each C file to a separate .wasm file, which means the command needed to perform the compilation step is verbose. To perform the build, open a terminal instance in your /parallel-wasm directory and run the following commands:

# First, compile the add.c file:
emcc -Os -s WASM=1 -s SIDE_MODULE=1 -s BINARYEN_ASYNC_COMPILATION=0 lib/add.c -o src/calc-add.wasm

# Next, compile the subtract.c file
emcc -Os -s WASM=1 -s SIDE_MODULE=1 -s BINARYEN_ASYNC_COMPILATION=0 lib/subtract.c -o src/calc-subtract.wasm

You should see two new files in the /src directory: calc-add.wasm and calc-subtract.wasm. With the required files in place, it's time to test out the application.