Method FetchDirectoryAsync

Sources/Shared/IO/EmscriptenFileStream.cpp:265–326

	}

	void EmscriptenFilePicker::FetchDirectoryAsync(Containers::Function<void(Containers::ArrayView<EmscriptenFileStream>)>&& callback)
	{
		if (_activeCallback) {
			// Another callback is already active, cancel this one
			callback({});
			return;
		}

		auto window = emscripten::val::global("window");
		if (emscripten::val("showDirectoryPicker").in(window)) {
			_supportsCancel = true;

			auto dirHandle = window.call<emscripten::val>("showDirectoryPicker").await();
			auto values = dirHandle.call<emscripten::val>("values"); // Async iterator
			auto prevSize = _files.size();
			while (true) {
				auto entry = values.call<emscripten::val>("next").await();
				if (entry["done"].as<bool>()) {
					break; // End of async iteration
				}

				auto entryValue = entry["value"];
				if (entryValue["kind"].as<std::string>() == "file") {
					_files.emplace_back(entryValue.call<emscripten::val>("getFile").await());
				}
			}

			// Exclude previously added files
			callback(arrayView(_files).exceptPrefix(prevSize));
			return;
		}

		_activeCallback = Death::move(callback);

		// Create file input element which will display a native file dialog
		auto document = emscripten::val::global("document");
		auto input = document.call<emscripten::val>("createElement", emscripten::val("input"));
		input.set("type", "file");
		input.set("style", "display:none");
		input.set("multiple", "multiple");
		input.set("webkitdirectory", "webkitdirectory");

		// http://perfectionkills.com/detecting-event-support-without-browser-sniffing
		_supportsCancel = false;
		if (emscripten::val("oncancel").in(input)) {
			_supportsCancel = true;
		} else {
			input.set("oncancel", emscripten::val("return;"));
			if (input["oncancel"].typeOf().as<std::string>() == "function") {
				_supportsCancel = true;
			}
		}

		input.set("onchange", emscripten::val::module_property("jsReadFiles"));
		input.set("oncancel", emscripten::val::module_property("jsCancelReadFiles"));
		input.set("data-callbackContext", emscripten::val(std::size_t(this)));

		auto body = document["body"];