I am trying to write a streamlined version of a XMLHttpRequest demo script shown here:
.asp?filename=tryajax_first
I'm only going to use this on iPad, so I don't have to check for older versions of IE, and so on. On button click, I want to check if the connection exists. Here's my entire html page, including JavaScript snippet:
<html>
<head>
<script>
var myURL = "";
function testConnection(url) {
var xmlhttp;
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
alert("Connected!");
} else {
alert("Not connected!");
}
}
xmlhttp.open("GET", url, true);
xmlhttp.send();
}
</script>
</head>
<body>
<button type="button" onclick="testConnection(myURL)">Test Connection</button>
</body>
</html>
For some weird reason, even though I'm online, when I click the button, I get repeated "Not connected" alerts, and only after a while I get the "Connected" alert, followed by no alerts.
Looks like I messed up, but I can't see where. What should I change to make it work?
I am trying to write a streamlined version of a XMLHttpRequest demo script shown here:
http://www.w3schools./ajax/tryit.asp?filename=tryajax_first
I'm only going to use this on iPad, so I don't have to check for older versions of IE, and so on. On button click, I want to check if the connection exists. Here's my entire html page, including JavaScript snippet:
<html>
<head>
<script>
var myURL = "http://www.google.";
function testConnection(url) {
var xmlhttp;
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
alert("Connected!");
} else {
alert("Not connected!");
}
}
xmlhttp.open("GET", url, true);
xmlhttp.send();
}
</script>
</head>
<body>
<button type="button" onclick="testConnection(myURL)">Test Connection</button>
</body>
</html>
For some weird reason, even though I'm online, when I click the button, I get repeated "Not connected" alerts, and only after a while I get the "Connected" alert, followed by no alerts.
Looks like I messed up, but I can't see where. What should I change to make it work?
Share Improve this question edited Jun 27, 2013 at 16:00 Givi 1,7342 gold badges21 silver badges35 bronze badges asked Jun 27, 2013 at 15:53 Dimitri VorontzovDimitri Vorontzov 8,11412 gold badges51 silver badges78 bronze badges1 Answer
Reset to default 3If you can use xhr2, you can learn stuff from this tutorial and rewrite your code to something like this:
function testConnection(url) {
var xmlhttp = new XMLHttpRequest();
xmlhttp.onload = function() { alert("Connected!"); }
xmlhttp.onerror = function() { alert("Not Connected"); }
xmlhttp.open("GET",url,true);
xmlhttp.send();
}
If you send request to another domain, you may get error even if it exists, if the target server has Same-Domain-Policy restriction (default). If the target server is on another domain, it must send header
Access-Control-Allow-Origin: *
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