Check whether a web resource exist or not

You can use HEAD requests to check whether a Web resource exists, and use up a lot less bandwidth doing so. The example code, exists.html, shows how this works by checking whether or not the data.txt file exists. The following example works by doing a HEAD request on that file, and checking the return Http status code — 200 means everything’s fine and the file is there, ready for use, but 404 means nope, file isn't there.

<script language = “javascript”>

var XMLHttpRequestObject = false;

if (window.XMLHttpRequest) {

XMLHttpRequestObject = new XMLHttpRequest();

} else if (window.ActiveXObject) {

XMLHttpRequestObject = new ActiveXObject(“Microsoft.XMLHttp”);

}

function getData(dataSource, divID)

{

if(XMLHttpRequestObject) {

var obj = document.getElementById(divID);

XMLHttpRequestObject.open(“HEAD”, dataSource);

XMLHttpRequestObject.onreadystatechange = function()

{

if (XMLHttpRequestObject.readyState == 4) {

if (XMLHttpRequestObject.status == 200) {

obj.innerHTML = “URL exists”;

}

else if (XMLHttpRequestObject.status == 404) {

obj.innerHTML = “URL does not exist”;

}

}

}

XMLHttpRequestObject.send(null);

}

}

</script>

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