Trying to make a progress bar for a form upload (old HTML4 form upload, not new HTML5 API). The progress actually tracks additional work being done after the file has moved. The way it has been designed is that the stream stays opened until after the additional work is done, and then the server-side method finally returns, which closes the stream.

I'm having some issues that may be specific to Chrome. I do also have a working implementation, but I'm hoping to get something "better".

For anybody who is likely to ask for code: it's intentionally not here. The scenario explains the problem; the code itself wasn't "at fault" and will just be more clutter.

Failed attempt #1 in a nutshell

1. Initiate form upload
2. Set interval on an Ajax call that grabs the progress in some JSON
3. Render the data to a progress bar

Reason for failure: the upload stream blocks other activity on the page, and you cannot make additional Ajax calls during the transfer.

Failed attempt #2 in a nutshell

1. Create an iFrame which contains the same Ajax calls
2. Render the data to an element within the iFrame (everything needed is self-contained and does not reference the "top" document in the least)

Result:

• before initiating the form upload, I could render "status: waiting" from the JSON. The rendering function also incremented a counter so I would see "attempt #X". The # of attempts would increment while status is waiting.

• after transfer initiated, the Ajax calls were successfully getting 200 and I could inspect the responses to see that the JSON was in fact there.

• HOWEVER, I could not update the "shadow DOM" (is that the correct term?) in the iFrame. Attempts to access nodes within the iFrame and modify them failed. Even the counter did not increment.

• When the transfer pleted, it would then successfully render "status: plete" and the counter would jump ahead (the counter was incrementing, but rendering it to the iFrame just wasn't working)

GRR!

Successful Attempt

The iFrame does not request Ajax anymore. The iframe's src attribute is set to a URL that returns a pre-rendered progress bar. The document being loaded into the iframe is set to reload itself. So at the prescribed interval, it re-renders a new progress bar which has "moved along".

The result is a "working" progress bar, although sometimes the lag in the request causes the iframe to be blank for a split second, which isn't my preference.

Can anybody think of a better way to do this? Is it possible that I could have the form itself in the iFrame and the Ajax work in the "top" document instead?

I mainly want to divide the presentation layer from the data layer, but as long as I have to return a rendered progress bar, that isn't going to work. As a bonus, if I can find a way to update the progress bar via Ajax, I won't have those "blank" blips.

Trying to make a progress bar for a form upload (old HTML4 form upload, not new HTML5 API). The progress actually tracks additional work being done after the file has moved. The way it has been designed is that the stream stays opened until after the additional work is done, and then the server-side method finally returns, which closes the stream.

I'm having some issues that may be specific to Chrome. I do also have a working implementation, but I'm hoping to get something "better".

For anybody who is likely to ask for code: it's intentionally not here. The scenario explains the problem; the code itself wasn't "at fault" and will just be more clutter.

Failed attempt #1 in a nutshell

1. Initiate form upload
2. Set interval on an Ajax call that grabs the progress in some JSON
3. Render the data to a progress bar

Reason for failure: the upload stream blocks other activity on the page, and you cannot make additional Ajax calls during the transfer.

Failed attempt #2 in a nutshell

1. Create an iFrame which contains the same Ajax calls
2. Render the data to an element within the iFrame (everything needed is self-contained and does not reference the "top" document in the least)

Result:

• before initiating the form upload, I could render "status: waiting" from the JSON. The rendering function also incremented a counter so I would see "attempt #X". The # of attempts would increment while status is waiting.

• after transfer initiated, the Ajax calls were successfully getting 200 and I could inspect the responses to see that the JSON was in fact there.

• HOWEVER, I could not update the "shadow DOM" (is that the correct term?) in the iFrame. Attempts to access nodes within the iFrame and modify them failed. Even the counter did not increment.

• When the transfer pleted, it would then successfully render "status: plete" and the counter would jump ahead (the counter was incrementing, but rendering it to the iFrame just wasn't working)

GRR!

Successful Attempt

The iFrame does not request Ajax anymore. The iframe's src attribute is set to a URL that returns a pre-rendered progress bar. The document being loaded into the iframe is set to reload itself. So at the prescribed interval, it re-renders a new progress bar which has "moved along".

The result is a "working" progress bar, although sometimes the lag in the request causes the iframe to be blank for a split second, which isn't my preference.

Can anybody think of a better way to do this? Is it possible that I could have the form itself in the iFrame and the Ajax work in the "top" document instead?

I mainly want to divide the presentation layer from the data layer, but as long as I have to return a rendered progress bar, that isn't going to work. As a bonus, if I can find a way to update the progress bar via Ajax, I won't have those "blank" blips.

• javascript

• Have you tried submitting the file upload to an iFrame which blocks nothing on the page but allows server requests to happen? Alos - depending on your restrictions - if you have access to HTML5 browsers there is a progress event on XHR objects now. But it's only supported by Chrome and Firefox (maybe Opera). Definitely not IE. – Brandon Buck Commented Apr 24, 2013 at 19:22
• Thanks, isuriel. I think that'll be something to try. I have not done so yet. The HTML5 progress event will give me access to the "move" portion, but I will still need to access the "post-move" progress from the server. But reversing the role of the iFrame might be a way to go. – Greg Pettit Commented Apr 24, 2013 at 19:28
• this one seem to have everything you require, in case you're using jQuery stackoverflow./questions/15410265/… – Oleg Mikheev Commented Apr 24, 2013 at 19:37
• Oleg, if I'm reading the code correctly, it's not going to handle the "after the file move" portion. It will just sit at 100% while the "extra" work is being done; this will work for the first leg of the transfer (moving the file) but it doesn't provide a mechanism for capturing the progress of the second leg (the extra work being done). – Greg Pettit Commented Apr 24, 2013 at 19:43

4 Answers 4

To expand on my ment and offer guidance, to perform the "hidden iframe file upload" you need to have a hidden frame (so obvious isn't it?) with a name.

<html>
  <body>
    <iframe name="file-upload" src="" style="border: none; visibility: hidden; width: 0; height: 0; position: absolute; top: 0; left: 0;"></iframe>
    The iframe shouldn't be visible, just pretend I didn't use inline styles though.
    <form id="uploadForm" action="anaction.php" enctype="whatever-you-need-here" method="post">
      File: <input type="file" /><br />
      <input type="submit" value="Upload" />
    </form>
  </body>
</html>

All pretty standard stuff so far. Next up es the Javascript:

var form = document.getElementById("uploadForm");
form.onsubmit = function() { 
  console.log("The form has been submitted, start progress!"); 
}
form.target = "file-upload"; // the name of the iframe
// Go about your business, when "Upload" is pressed the file will be submitted
// to the iframe so you'd start your progress requests on form submit.

Ignore the poor practices, it's a simple example.

honestly I do all the front end dev for an app and I was looking for the same thing. First i tried just using our socket.io to send back a number which i then turned into a percentage. I'd then apply that to the twitter bootstrap prog bar.

What i ended up doing and sticking with was using fine uploader http://fineuploader./ The documentation kinda sucks and you'll have to toy with it a little bit but it has a built in event that fires over and over while uploading something that will actually return you the progress.

I decided to use: http://blueimp.github.io/jQuery-File-Upload/ because it is free and gives you nice progress bar.

The last time I did it I just submitted the form with data to some invisible iframe, then I could just forget about it.

Next I started polling some URL/REST API for progress.

Once the submit is done - an event will fire, its handler will stop progress polling.

I don't see any problem with this approach, but for some reason neither of yours seem to match what I'm describing, so I'm putting it as an answer.

If you use jQuery the best approach would be to "ajaxify" your form using jQuery Form plugin. You can refer to this question for the example: File upload progress bar with jQuery.