javascript - Preload image doesn't always appear -

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i have created simple ajax request:

             var params = "postdata=" + mydata;              if (window.xmlhttprequest) {                  xmlhttp = new xmlhttprequest();              } else {                  xmlhttp = new activexobject("microsoft.xmlhttp");              }              xmlhttp.onreadystatechange = function () {                  if (xmlhttp.readystate == 4 && xmlhttp.status == 200) {                      document.getelementbyid("data").innerhtml = xmlhttp.responsetext;                  }              }              xmlhttp.open("post", "data.php", true);              xmlhttp.setrequestheader("content-type", "application/x-www-form-urlencoded");              xmlhttp.setrequestheader("content-length", params.length);              xmlhttp.setrequestheader("connection", "close");              xmlhttp.send(params);

and html code:

    <div id="data">     <img src="/images/preload.gif" />     <b style="color:#9ca6dc;font-size:12px;">wait</b>     </div>

the problem preload.gif , "wait" text appears , not always.

why ? how can resolve ?

the explanation ajax request works see content (as alessandro pezzato said). if don't see readystate of xmlhttp request had change.

or have other javascript runs asynchronously , changes on same content.


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