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”>
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var XMLHttpRequestObject = false;
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if (window.XMLHttpRequest) {
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XMLHttpRequestObject = new XMLHttpRequest();
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} else if (window.ActiveXObject) {
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XMLHttpRequestObject = new ActiveXObject(“Microsoft.XMLHttp”);
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}
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function getData(dataSource, divID)
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{
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if(XMLHttpRequestObject) {
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var obj = document.getElementById(divID);
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XMLHttpRequestObject.open(“HEAD”, dataSource);
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XMLHttpRequestObject.onreadystatechange = function()
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{
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if (XMLHttpRequestObject.readyState == 4) {
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if (XMLHttpRequestObject.status == 200) {
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obj.innerHTML = “URL exists”;
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}
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else if (XMLHttpRequestObject.status == 404) {
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obj.innerHTML = “URL does not exist”;
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}
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}
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}
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XMLHttpRequestObject.send(null);
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}
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}
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