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I was working on Ajax web application last time, and realized that we cannot upload a File using Ajax. I saw it on many sites, and tutorials saying we cannot upload a file using Ajax, for that we need to use Flash or iframe's etc..to do so. But why it is not possible? In future will that be possible?

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"Flash of iframe's"?? :) – Mayank Jan 19 '11 at 7:17
@Mayank oops! :D – Harish Kurup Jan 19 '11 at 7:21
Move to StackOverflow? – NickC Jan 19 '11 at 8:04
@Renesis actually i am not looking for the code..or help in coding for now just a discussion on why? – Harish Kurup Jan 19 '11 at 8:07

3 Answers

up vote 6 down vote accepted

Uploading files is deliberately hard to avoid security leaks. If you could do that with a few lines of JavaScript, evil websites could secretly upload local files. For that reason, it must be done through a form, the user must see a file upload control, must choose the file by himself. After that, the form has to be submitted, and that's normal HTTP transfer, not Ajax, because XMLHttpRequest doesn't support multipart/form-data uploads. Therefore the iframes to gather the result. But those iframes can be invisible, and they can be processed after loading.

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ok i got that, Ajax also does a HTTP transfer i think, and but my question was can we do file upload through forms using Ajax method. like we have a file upload element and send that file data using XMLHttpRequest object. – Harish Kurup Jan 19 '11 at 7:53
just edited my answer regarding that question - XMLHttpRequest doesn't support multipart/form-data uploads, so you can't. What's the problem? The method using iframes works well, doesn't it? – user281377 Jan 19 '11 at 7:55
just found this link, seems like FF can do a bit more - but that's not crossplattform, so think it's relatively useless by now: igstan.ro/posts/… – user281377 Jan 19 '11 at 7:59
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Actually, you could still do a file transfer via a PUT or POST (even manually encoding the multipart/form-data). The reason you can't do file uploads via Ajax is because browsers restrict access to the local filesystem: you can't get to the contents of the file the user selected via javascript, so you can't upload it. – Dean Harding Jan 19 '11 at 8:01
Dean: true, thanks for the correction, though it's not a file transfer if there is no file to be transfered ;-) – user281377 Jan 19 '11 at 8:11
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up vote 2 down vote

Well you can do that right now using JQuery Form Plugin. Have a look at the demos here - http://jquery.malsup.com/form/

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but the plugins might be using some iframes or flash..and not purely through Ajax..i think..cos we were using Uploadify. @Mayank but r u sure?? – Harish Kurup Jan 19 '11 at 7:24
@Harish I am pretty sure that there is no flash involved as jQuery is pure javascript and also because I have used it. Have a look at my answer here - stackoverflow.com/questions/4625377/… – Mayank Jan 19 '11 at 7:28
can u tell how to do it without jQuery i.e in core Javascript.(sorry not doubting u, i am confused need to get out..) – Harish Kurup Jan 19 '11 at 7:32
@Harish I am not sure what you mean by "core javascript". "jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JavaScript." – Mayank Jan 19 '11 at 8:21
i was talking about the XMLHttpRequest object and not jQuery, the question was why we can't use Ajax to upload a file! – Harish Kurup Jan 19 '11 at 8:32
up vote 1 down vote

Upload support is part of the XMLHttpRequest Level 2 Working Draft. It's currently supported by Safari and Chrome, and should be supported later in the year by new versions of Firefox and Internet Explorer.

XHR2 Browser Support Table

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thanks for the Updates.. – Harish Kurup Jan 19 '11 at 9:12

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