how to pass a struct to emscripten::val::call function

[aharondavid]

if we want to replace that JS code by c++, how can we pass the {willReadFrequently: true} value:
JS:
const ctx = canvas.getContext('2d', {willReadFrequently: true});

C++:
emscripten::val.call<emscripten::val>("getContext", std::string("2d"),_**what should be here?**_);