You can wrap JavaScript code inside your C/C++ file with EM_ASM() and it will execute when the compiled code is run in the browser. The following code demonstrates basic usage:

#include <emscripten.h>

int main() {
    EM_ASM(
        console.log('This is some JS code.');
    );
    return 0;
}

The JavaScript code is executed immediately and cannot be reused within the C/C++ file in which it is contained. Arguments can be passed into the JavaScript code block where they arrive as variables $0, $1, and so on. These arguments can either be of type int32_t or double. The following code snippet, taken from the Emscripten site, demonstrates how to utilize arguments in an EM_ASM() block:

EM_ASM({
    console.log('I received: ' + [ $0, $1 ]);
}, 100, 35.5);