The terms "exports" and "imports" are commonly meant relative to the WebAssembly instance. In other words, an "export" makes a compiled C/C++ function callable from JavaScript; an "import" makes a JavaScript function callable from compiled C/C++ code.
This most basic example uses plain C (doesn't use the C standard library). It only exports functions
to the browser runtime (it doesn't import any functions from the runtime). It compiles two C
functions (add and subtract), defined in separate files, and links them into a single WASM
binary. Both functions are called from plain ES8/JavaScript (doesn't use any libraries), and the two
results (42 and 42) are printed to the browser console.
The C functions need to be given visibility by setting their compiler attribute visibility to
default, otherwise they will not be exported.