jenyayel/pinger.htm

## pinger.htm
<!DOCTYPE html>
<html>
<head>
    <title>Pinger</title>
</head>
<body>
    <a href="#">return back</a>
    <hr />
    <pre></pre>
    <script src="pinger.js"></script>
</body>
</html>

## pinger.js
(function () {
    var _options = {
        pingUrl: getQuery('pingUrl'),
        frequency: parseInt(getQuery('frequency') || 10), // in seconds
        returnUrl: getQuery('returnUrl') || document.referrer,
        stopAfterFail: parseInt(getQuery('stopAfterFail') || 3), // after which failure to stop
        strategy: getQuery('strategy') || 'xhr'
    };


    if (!validateInput(_options))
        return;

    document.getElementsByTagName('a')[0].onclick = () => {
        window.location.href = _options.returnUrl;
        return false;
    };

    var strategy = _options.strategy === 'xhr' ? xhrStrategy : iframeStrategy;

    l(`Starting pinging with frequency ${_options.frequency} seconds using "${_options.strategy}" strategy...`);
    var pending = false, failCount = 0;

    var timer = setInterval(() => {
        if (pending === true) {
            l('Skipping scheduled ping since there is another one still pending');
            return;
        }
        pending = true;

        l('Sending request...');
        strategy(_options.pingUrl, (result) => {
            pending = false;
            if (result.success) failCount = 0;
            else failCount += 1;

            l(`Request ${result.success ? 'done' : 'failed'}`, result.data);

            if (failCount === _options.stopAfterFail) {
                clearInterval(timer);
                l(`Stopped pinging after ${failCount} failed attempts in a row.`);
            }
        });
    }, _options.frequency * 1000);

    function xhrStrategy(url, callback) {
        var xhr = new XMLHttpRequest();
        xhr.withCredentials = true;
        xhr.open('GET', url);
        xhr.onreadystatechange = () => {
            if(xhr.readyState !== 4) return;
            if (typeof callback === 'function'){
                callback({
                    success: xhr.status === 200,
                    data: { status: xhr.status, body: xhr.responseText }
                });
            }
        };
        xhr.send(null);
    }

    function iframeStrategy(url, callback) {
        var iframe = document.createElement('iframe');
        iframe.style.display = 'none';
        iframe.onload = (event) => {
            if (typeof callback === 'function') {
                callback({
                    success: true,
                    data: event
                });
            }
            iframe.remove();
        };

        iframe.setAttribute("src", url);
        document.body.appendChild(iframe);
    }

    function validateInput(options)
    {
        if (!options.pingUrl) {
            l('"pingUrl" is missing', options);
            return false;
        }

        if (options.returnUrl === '') {
            l('"returnUrl" or referrer is missing', options);
            return false;
        }

        if (isNaN(options.frequency)) {
            l('"frequency" must be a number', options);
            return false;
        }

        if (isNaN(options.stopAfterFail)) {
            l('"stopAfterFail" must be a number', options);
            return false;
        }

        if (options.strategy !== 'iframe' && options.strategy !== 'xhr') {
            l('"strategy" must be either "iframe" or "xhr"', options);
            return false;
        }

        return true;
    }

    function l(message, params)
    {
        var _output = document.getElementsByTagName('pre')[0];
        _output.innerHTML += message;
        if (params)
            _output.innerHTML += ' > ' + JSON.stringify(params);

        _output.innerHTML += '<br>';
    }

    function getQuery(name) {
        var query = window.location.search.substring(1);
        var vars = query.split('&');
        for (var i = 0; i < vars.length; i++) {
            var pair = vars[i].split('=');
            if (decodeURIComponent(pair[0]) == name)
                return decodeURIComponent(pair[1]);
        }
        return false;
    }
})();
	<!DOCTYPE html>
	<html>
	<head>
	<title>Pinger</title>
	</head>
	<body>
	<a href="#">return back</a>
	<hr />
	<pre></pre>
	<script src="pinger.js"></script>
	</body>
	</html>
	(function () {
	var _options = {
	pingUrl: getQuery('pingUrl'),
	frequency: parseInt(getQuery('frequency') \|\| 10), // in seconds
	returnUrl: getQuery('returnUrl') \|\| document.referrer,
	stopAfterFail: parseInt(getQuery('stopAfterFail') \|\| 3), // after which failure to stop
	strategy: getQuery('strategy') \|\| 'xhr'
	};


	if (!validateInput(_options))
	return;

	document.getElementsByTagName('a')[0].onclick = () => {
	window.location.href = _options.returnUrl;
	return false;
	};

	var strategy = _options.strategy === 'xhr' ? xhrStrategy : iframeStrategy;

	l(`Starting pinging with frequency ${_options.frequency} seconds using "${_options.strategy}" strategy...`);
	var pending = false, failCount = 0;

	var timer = setInterval(() => {
	if (pending === true) {
	l('Skipping scheduled ping since there is another one still pending');
	return;
	}
	pending = true;

	l('Sending request...');
	strategy(_options.pingUrl, (result) => {
	pending = false;
	if (result.success) failCount = 0;
	else failCount += 1;

	l(`Request ${result.success ? 'done' : 'failed'}`, result.data);

	if (failCount === _options.stopAfterFail) {
	clearInterval(timer);
	l(`Stopped pinging after ${failCount} failed attempts in a row.`);
	}
	});
	}, _options.frequency * 1000);

	function xhrStrategy(url, callback) {
	var xhr = new XMLHttpRequest();
	xhr.withCredentials = true;
	xhr.open('GET', url);
	xhr.onreadystatechange = () => {
	if(xhr.readyState !== 4) return;
	if (typeof callback === 'function'){
	callback({
	success: xhr.status === 200,
	data: { status: xhr.status, body: xhr.responseText }
	});
	}
	};
	xhr.send(null);
	}

	function iframeStrategy(url, callback) {
	var iframe = document.createElement('iframe');
	iframe.style.display = 'none';
	iframe.onload = (event) => {
	if (typeof callback === 'function') {
	callback({
	success: true,
	data: event
	});
	}
	iframe.remove();
	};

	iframe.setAttribute("src", url);
	document.body.appendChild(iframe);
	}

	function validateInput(options)
	{
	if (!options.pingUrl) {
	l('"pingUrl" is missing', options);
	return false;
	}

	if (options.returnUrl === '') {
	l('"returnUrl" or referrer is missing', options);
	return false;
	}

	if (isNaN(options.frequency)) {
	l('"frequency" must be a number', options);
	return false;
	}

	if (isNaN(options.stopAfterFail)) {
	l('"stopAfterFail" must be a number', options);
	return false;
	}

	if (options.strategy !== 'iframe' && options.strategy !== 'xhr') {
	l('"strategy" must be either "iframe" or "xhr"', options);
	return false;
	}

	return true;
	}

	function l(message, params)
	{
	var _output = document.getElementsByTagName('pre')[0];
	_output.innerHTML += message;
	if (params)
	_output.innerHTML += ' > ' + JSON.stringify(params);

	_output.innerHTML += '<br>';
	}

	function getQuery(name) {
	var query = window.location.search.substring(1);
	var vars = query.split('&');
	for (var i = 0; i < vars.length; i++) {
	var pair = vars[i].split('=');
	if (decodeURIComponent(pair[0]) == name)
	return decodeURIComponent(pair[1]);
	}
	return false;
	}
	})();