Platform: this is all wrong anyway and mainLoopIteration() is useless.

The exec() should return int to be API-compatible with other
implementations.

src/Magnum/Platform/EmscriptenApplication.cpp

@@ -549,17 +549,15 @@ EmscriptenApplication::GLConfiguration::GLConfiguration():
     _colorBufferSize{8, 8, 8, 0}, _depthBufferSize{24}, _stencilBufferSize{0} {}
 #endif
 
-void EmscriptenApplication::mainLoopIteration() {
-    if(!(_flags & Flag::Redraw)) return;
+int EmscriptenApplication::exec() {
+    emscripten_set_main_loop_arg([](void* userData) {
+        auto& app = *static_cast<EmscriptenApplication*>(userData);
+        if(!(app._flags & Flag::Redraw)) return;
 
-    _flags &= ~Flag::Redraw;
-    drawEvent();
-}
-
-void EmscriptenApplication::exec() {
-    emscripten_set_main_loop_arg([](void* arg) {
-        static_cast<EmscriptenApplication*>(arg)->mainLoopIteration();
+        app._flags &= ~Flag::Redraw;
+        app.drawEvent();
     }, this, 0, true);
+    return 0;
 }
 
 void EmscriptenApplication::exit(int) {

src/Magnum/Platform/EmscriptenApplication.h

@@ -292,33 +292,23 @@ class EmscriptenApplication {
         EmscriptenApplication& operator=(EmscriptenApplication&&) = delete;
 
         /**
-         * @brief Execute main loop
+         * @brief Execute the application
          *
-         * Calls @ref mainLoopIteration() in a loop until @ref exit() is
+         * Sets up Emscripten to execute event handlers until @ref exit() is
          * called. See @ref MAGNUM_EMSCRIPTENAPPLICATION_MAIN() for usage
          * information.
          */
-        void exec();
+        int exec();
 
         /**
          * @brief Exit application main loop
-         * @param exitCode Exit code for compatibility with other application
-         *                 implementations
          *
-         * Stops main loop started by @ref exec().
+         * Stops execution started by @ref exec(). The @p exitCode is ignored
+         * and present only for API compatibility with other app
+         * implementations.
          */
         void exit(int exitCode = 0);
 
-        /**
-         * @brief Run one iteration of application main loop
-         *
-         * Called internally from @ref exec(). If you want to have better
-         * control over how the main loop behaves, you can call this function
-         * yourself from your own `main()` function instead of it being called
-         * automatically from @ref exec() / @ref MAGNUM_EMSCRIPTENAPPLICATION_MAIN().
-         */
-        void mainLoopIteration();
-
     protected:
         /* Nobody will need to have (and delete) EmscriptenApplication*, thus
            this is faster than public pure virtual destructor */