Update progress bar during emscripten webassembly is running?

I want to show a progress bar during an emscripten webassembly is running. But the progress bar is updatet AFTER the webassembly is finished. Is there a way to either interrupt webassembly (main thread) and then continue or force javascript (main thread) to render the GUI?

main.js

Module.cwrap('calc', 'undefined', [])();

calc.cpp

void calc() {
   EM_ASM({ progressBar($0); }, value); // here the progress bar should be updated immedately
   ...
   calc something
   ...
}
// but it's updated only here

I also tried it with

progressbar(val) {
   setTimeout(function(){ updateBar(val); }, 0);
}

Unfortunately for me it's not possible to use a webworker in a seperate file. Thanks...

@schteppe: Thxs! For who have the same issue. I solved it with emscripten_async_call().

main.js

Module.cwrap('calc', 'undefined', [])();

calc.cpp

void calc() {
   EM_ASM({ progressBar($0); }, value);
   emscripten_async_call("calcfunction, NULL, msec");
}
void calcfunction() {
   ...
   calc something
   ...
}