add a note on EXPORTED_FUNCTIONS mattering on the comple to JS stage #3759

site/source/docs/getting_started/FAQ.rst

@@ -255,6 +255,11 @@ To make sure a C function remains available to be called from normal JavaScript,
 
 	./emcc -s EXPORTED_FUNCTIONS="['_main', '_my_func']"  ...
 
+.. note:: 
+
+   `EXPORTED_FUNCTIONS` affects compilation to JavaScript. If you first compile to an object file,
+   then compile the object to JavaScript, you need that option on the second command.
+
 If your function is used in other functions, LLVM may inline it and it will not appear as a unique function in the JavaScript. Prevent inlining by defining the function with :c:type:`EMSCRIPTEN_KEEPALIVE`: ::
 
 	void EMSCRIPTEN_KEEPALIVE yourCfunc() {..}

site/source/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.rst

@@ -65,6 +65,13 @@ home directory::
 
     ./emcc tests/hello_function.cpp -o function.html -s EXPORTED_FUNCTIONS="['_int_sqrt']"
 
+.. note::
+
+   `EXPORTED_FUNCTIONS` affects compilation to JavaScript. If you first compile to an object file,
+   then compile the object to JavaScript, you need that option on the second command. If you do
+   it all together as in the example here (source straight to JavaScript) then this just works,
+   of course.
+
 After compiling, you can call this function with :js:func:`cwrap` using the
 following JavaScript::