Return a String from C++ to WASM

gistfile1.txt

// C++ bit . save it in an example.cpp file
#include "emscripten.h"
extern "C" { 
 inline const char* cstr(const std::string& message) {
    char * cstr = new char [message.length()+1];
    std::strcpy (cstr, message.c_str());
    return cstr;
}
	EMSCRIPTEN_KEEPALIVE
	const char* getAMessage() {
		return cstr("oh hai there!");
	};
  }
  
//create the HTML / JS bit
  
<script src="./a.out.js"></script>
<script>
  Module.onRuntimeInitialized = async _ => {
    const api = {
      message: Module.cwrap('getAMessage', 'string', []),
    };
    console.log(api.message());
  };
</script>

// compile with
emcc -s EXTRA_EXPORTED_RUNTIME_METHODS='["cwrap"]' -std=c++11 example.cpp