在重定向之前将有关已点击链接的信息发送到服务器

Question

We're creating a click tracking app, that builds heatmaps. I'm writing a script which users are suppose to insert into their pages for tracking to work.

It works fine on elements, which doesn't require a redirect or form submit. For example, if I click on h1 or p or whatever, it works perfectly correct. But, if I click on a a , request to our server never happens before the normal redirect.

In the last couple of days I tried a lot of ways to do that. First of, I tried a normal AJAX call, since it was a cross-domain request I had to use JSONP, but again, that AJAX call did not have time to execute before the redirect. Adding async: false would have solved the problem, but it doesn't work with JSONP requests. So I decided to add a flag variable which indicates that it is safe to move on with redirect and used an empty while loop to wait until it becomes try in the ajax callback. But the while loop was blocking the execution flow, so callback never got a chance to set that variable to true . Here is some simplified code:

$(document).on('click', function (e) {
    //part of the code is omitted 
    $.ajax({
        url: baseUrl,
        data: data,
        type: "get",
        dataType: "jsonp",
        crossDomain: true,
        complete: function (xhr, status,) {
            itsSafeToMoveOn = true;
        }
    });

    while(!itsSafeToMoveOn){}

    return true;
});

The next thing I tried is to use unload page event to wait until total ajax calls in progress would become zero (I had a counter implemented) and then to move on with redirect. It worked in Firefox and IE, but in WebKit there was this error:

Error: Too much time spent in unload handler

After that I realized that I don't care about the server response and using img.src for the request would be an ideal fit for this case. So at this point code looks like this:

$(document).click(function (e) {
    //part of the code is ommited
    (new Image).src = baseUrl + '?' + data;

    if (tag === "a" || clickedElement.parents().has("a")) {
        sleep(100); 
    }

    return true;
});

That way I increased the overall script performance slightly, but problem with links remains unchanged. The sleep function appears to be also blocking the execution flow and request never happens.

The only idea left is to return false from the event handler and than redirect manually to the clicked element's href or to call submit() on the form, but it will complicate things to much and believe me it's already a huge pain in the ass to debug this script in different browsers.

Does anyone have any other ideas?

Answer 1

var globalStopper = true;

$(document).on('click', function (e) {
    if (globalStopper === false)
        return true; //proceed with click if stopper is NOT set
    else {
        globalStopper = false; //release the breaks

        $.ajax({
            //blahblah
            complete: function (xhr, status,) {
                $(elem).click(); //when ajax request done - "rerun" the click
            }
        });
        return false; //DO NOT let browser process the click
    }
});

Also, instead of adding image, try adding script. And then add the script to the HEAD section. This way the browser will "wait" until it's loaded.

 $(document).on('click', function (e) {
     var scriptTag = document.createElement("script");
     scriptTag.setAttribute("type", "text/javascript");
     scriptTag.setAttribute("src", url);
     document.getElementsByTagName("head")[0].appendChild(scriptTag);
     return true;
 }

Answer 2

I would take a look at the navigator sendBeacon API mentioned in this stack overflow answer or directly linked to here .

From the description on the site

navigator.sendBeacon(url, data) - This method addresses the needs of analytics and diagnostics code that typically attempts to send data to a web server prior to the unloading of the document.

Answer 3

So if I understand right, you want your ajax logs completed before the page unloads and follows a link href. This sounds like a perfect case where you could consider using Deferreds in jQuery.

When your user clicks on anything that's supposed to take him away from the page, just check your promise status. If it's not resolved, you could throw a modal window over the page, and ask the user to wait til the progress is complete. Then, add a new pipe to your deferred , telling it to change the location href once everything is complete.

Let me know if this is the scenario. If it is, I'll explain in more detail. No use continuing if I didn't understand your requirement properly

Answer 4

You can save information to ajax request in cookies or localStorage and make any worker that will send information. Saving to cookies or localStorage is faster then ajax-request. You can do next:

$(document).click(function (e) {
    var queue = localStorage.getItem('requestQueue');
    queue.push(data);
    localStorage.setItem('requestQueue',queue);
});

$(function(){
  setInterval(function(){
    var queue = localStorage.getItem('requestQueue');
    while (queue.length > 0) {
      var data = queue.pop();
      $.ajax({
        ...
        success: function(){
          localStorage.setItem('requestQueue', queue);
        }
      });
    }
  },intervalToSendData);
});

So, when user click on link or send a form, data will be saved to storage and after user go to next page, this worker starts and send data to your server.

Answer 5

The JavaScript is basically executed in single thread. It is not possible to have your callback function executed and at the same time have an infinite loop waiting for a flag variable from it. The infinite loop will occupy the single execution thread and the callback will never be called.

Best approach is to cancel the default handler of your event and bubbling for it (basically return false if you are really building your tracking code with jQuery), and do the necessary actions (redirect page to the necessary address if a link was clicked or trigger other default actions), but this would take a lot of careful work to recreate all the possible combinations of actiona and callbacks.

Another approach is to: 1) Look for something specific to your code in the event data 2) If it is not present - make an AJAX call and in its callback re-trigger the same even on the same element, but this time with your specific bit added to the even data; after the AJAX call return false 3) If your specific bits are present in the data - simply do nothing, allowing the default event processing to take place.

The either approach may bite, however.