cib demo: C++ and JS calling into each other

main.cpp

#include <emscripten.h>

int counter = 0;
bool running = false;

// Defined in javascript
extern "C" void enableButtons();
extern "C" void setCounterValue(int);

// Called by javascript
extern "C" void run(bool r) {
    running = r;
}

// Called by javascript
extern "C" void reset() {
    counter = 0;
    setCounterValue(counter);
}

void timer(void *) {
    if(running)
        setCounterValue(counter++);
    emscripten_async_call(timer, nullptr, 200);
}

int main() {
    enableButtons();
    timer(nullptr);
}

main.html

%init-scripts%

<button id="run" onclick="wasmExports.run(true)" disabled>Run</button>
<button id="stop" onclick="wasmExports.run(false)" disabled>Stop</button>
<button id="reset" onclick="wasmExports.reset()" disabled>Reset</button>
<br />Counter value:
<span id="counter">0</span>

<script>
    wasmImports = {
        enableButtons() {
            document.getElementById('run').disabled = false;
            document.getElementById('stop').disabled = false;
            document.getElementById('reset').disabled = false;
        },
        setCounterValue(v) {
            document.getElementById('counter').textContent = v;
        },
    }
</script>