[flohofwoe]

I think emscripten does this by keeping dictionaries on the Javascript side which map numeric "ids" (used on the asm.js/wasm side) to JS objects. This is how mapping a GLuint 'texture id' to WebGL objects works for instance. The JS object won't be garbage collected as long as it 'pinned' in the lookup dictionary, but as soon as the asm.js/wasm side manually release the handle, the JS object will be GC'd. Future APIs (like the a WebGL successor) will hopefully provide 'garbage free' APIs so that they don't require keeping such helper structures around.