Can EM_JS return complex values?

Question

I'm writing some WebAssembly code using the emscripten macro EM_JS. The javascript code inside the macro returns an array of bytes but by the time the C++ code gets it, it's just pointer so it doesn't know how many elements are actually in the array. So I need a way to return the array and its length.

EM_JS(const char*, RunJsFunction, (const char* inBytes), {
    const outBytes = myMethod(inBytes);
    return outBytes; // this turns into a raw pointer in C++
});

const char someBytes[3] = { 1, 2, 3};
const char* result = RunJsFunction(someBytes); // no idea how many bytes are in result

I came up with a hacky solution that involves the C++ code passing in an array of two elements that the javascript can use as a container to "return" some data to the C++ function. One element is used contain the pointer to the array that I want to return and the other contains its length. Kind of like return an object { arrayHead: 0x123abc, length: 5 } but using an array instead. Anyway, it works but it's grody to the max.

EM_JS(void, CallWriteSerial, (const char* inBytes, const int* outArray), {
    const res = myMethod(inBytes);
    outArray[0] = res.pointer;
    outArray[1] = res.length;
});

const char inBytes[5] = { 1, 2, 3, 4, 5 };
int output[2];
CallWriteSerial(inBytes, output);

// output is an array containing two elements, a pointer to the resulting byte array and its length
const char* outBytes = (const char*)output[0];
const int length = output[1];

Is there a better way to do this?