extensions/typescript-language-features/web/webServer.ts/createWebSystem
function createWebSystem(args: string[]) {
	(ts as any).Debug.assert(ts.sys === undefined);
	const webHost: WebHost = {
		readFile: webPath => {
			const request = new XMLHttpRequest();
			request.open('GET', webPath, /* asynchronous */ false);
			request.send();
			return request.status === 200 ? request.responseText : undefined;
		},
		fileExists: webPath => {
			const request = new XMLHttpRequest();
			request.open('HEAD', webPath, /* asynchronous */ false);
			request.send();
			return request.status === 200;
		},
		writeMessage,
	};
	// Do this after sys has been set as findArguments is going to work only then
	const sys = serverCreateWebSystem(webHost, args, () => findArgument('--executingFilePath') || location + '');
	setSys(sys);
	const localeStr = findArgument('--locale');
	if (localeStr) {
		validateLocaleAndSetLanguage(localeStr, sys);
	}
}