Question

I’m developing a javascript code to run on an embedded device using the ANT Galio browser.

Ideally, I’d like the code to make a get request to another server. After that get request is made, the page would not allow the user to submit another get request, until a response had been received from the previous get request.

For some reason sometimes I am receiving a readyState of 4 almost instantly. It is as though it is evaluating the previous XmlHttpRequest object and not the new one. What am I doing wrong?

 <script type="text/javascript">

var fail= function (env, resp, stat) {

        alert(resp);
};
var succ= function (env, resp) {
};

var canScan = true;

/* start scan */
function scan (name) {
        if (canScan) {
                //deactivate button
                deactivateScanButtons();
                //let server know
                ajax = new XMLHttpRequest();
                var scanUrl = 'http://19X.1XX.X.XX:8080/scan/' + name
                ajax.open('GET', scanUrl, true);
                ajax.onreadystatechange = function() {
                        if (ajax.readyState==4) {
                                //allow button to work again
                                activateScanButtons();
                                alert("ready state 4");


                        };
                };

                ajax.send();
//initiate scan
                xrxScanInitiateScan(
                        'http://127.0.0.1',
                        "ftp.xst",
                        false,
                        succ,
                        fail);
        }

}

function deactivateScanButtons () {
//      canScan = false;

        var indicator = document.getElementById('buttons');
        indicator.style.visibility = "hidden";
}
function activateScanButtons () {
//      canScan = true;

        var indicator = document.getElementById('buttons');
        indicator.style.visibility = "visible";

}
</script>

Answer 1

3 suggestions:

1. To avoid any caching on the client side, add a randomly generated number, or the current timestamp to the request querystring.
2. As Yoni said, initiate your XMLHttpRequest object with var keyword.
3. For each request, save the current timestamp within a global variable. In onreadystatechange, call activateScanButtons only if the global timestamp matches the corresponding timestamp of that given request. This way, only the latest request will be able to call activateScanButtons.