To test on another domain, put this code in <script> tag:

window.onload = function () {
	document.getElementById('ajax').onclick = function () {
		var xhr = new XMLHttpRequest();
		xhr.open('GET', 'http://localhost:12345/');
		xhr.send();
		xhr.onreadystatechange = function () {
			if (xhr.readyState === 4) {
				if (xhr.status === 200 && window.location.protocol === 'file:') {
					alert('Test passed, the request from local file system not blocked');
				} else if (xhr.status !== 200 && window.location.protocol !== 'file:') {
					alert('Test passed, the request from another domain is blocked');
				} else {
					alert('Test not passed, something gone wrong');
				}
			}
		};
	};

document.getElementById('ws').onclick = function () {
		var socket = new WebSocket('ws://localhost:12345/echo', ['echo']);
		socket.onerror = function () {
			if (window.location.protocol !== 'file:') {
				alert('Test passed, the request from another domain is blocked');
			} else {
				alert('Test not passed, something gone wrong');
			}
		};
		socket.onopen = function () {
			socket.send('echo');
		};
		socket.onmessage = function (event) {
			alert('Test passed, the request from local file system not blocked and a message is received back');
			socket.close();
		};
	};
};

and this one in <body> tag:

To test in this local file system, press the buttons: