Shaun Mccran

My digital playground


Uploading an image and previewing the thumbnail in one hit

A recent piece of functionality required a user to be able to upload an image, and view a thumbnail of that image alongside all the other related details that they were entering (item specific data etc).

After having a look through several forums it seemed that people's opinions were split on whether this could be accomplished using Ajax at all. So I decided to go old school and use an iFrame. I'm not a big fan of frames in any incarnation, but in this case I was willing to make an exception.

So firstly there is an upload form. It is a pretty standard ColdFusion form. Just remember when uploading a file to set the enctype="multipart/form-data". Also the submit button does not submit the form, it fires a JavaScript function 'changeFrame()'. The JavaScript function sets the target of the form submission to the iFrame, and then submits it.

view plain print about
2    <iframe id="uploadFrame" name="uploadFrame" src="action.cfm" height="110" width="90" scrolling="no" frameborder="0"></iframe>
4<form name="uploader" action="action.cfm" method="post" enctype="multipart/form-data">
5        <input type="file" name="image" size="5">
6        <input type="button" name="action" value="Upload" onclick="changeFrame()"/>
7    </form>
11function changeFrame()
12    {
13        document.getElementById('uploader').target = 'uploadFrame';
14        document.getElementById('uploader').submit();
15    }

The form submits to the 'action.cfm' template. This template displays a placeholder image thumbnail initially, but when the form is submitted it performs the file upload using cffile, then displays the newly uploaded file instead of the placeholder. Ideally at this point I would like to resize the image with cfimage, but my hosting company is still using ColdFusion 7, so I may have to use a third party tag to do the same.

view plain print about
1<body style="margin: 0;">
2<cfset dest = "webroot/root/tmp/">
4<cfif isdefined('form.image')>
5    <cffile action="upload" filefield="form.image" destination="#dest#" nameconflict="makeunique">
6    <cfset variables.img = cffile.clientFile>
8    <cfset variables.img = "holder.gif">
12<cfoutput><img src="tmp\#variables.img#" height="100" width="75" border="1"></cfoutput>

It is a shame I had to use an iFrame, and it would be really interesting to see if this is possible in a more web 2.0 scripted way.

Comments (Comment Moderation is enabled. Your comment will not appear until approved.)
todd sharp's Gravatar There is no way to do file upload in ajax without using some sort of hack. Your best bet is to use a hidden SWF file to handle the upload if you want to stick with an HTML front end (as opposed to creating an uploader in Flash/Flex). jQuery has an uploader in the UI project - you might check it out (

For resizing check out image.cfc by Rick Root.
# Posted By todd sharp | 14/10/2009 13:42
Shaun McCran's Gravatar Hi, Thanks for the tip on the JQuery uploader, I'll check it out, I'd really like to get away from the iFrame. I'd never really thought about doing it in Flex, probably because it is part of a larger form, and there is no real reason to use Flex for the rest of it. Worth exploring as an option though.
# Posted By Shaun McCran | 15/10/2009 09:50
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