Javascript returns wrong file size, when using ASP.NET (aspx pages) for uploading

Question

I am uploading a file in an ASP.NET application, I need to get the file size for some client side validation. Following the advice I found here. I have something like this:

in aspx:

<td class="form_input_bold">
            <asp:FileUpload Width="80%" ID="fuUploadFile" CssClass="button" runat="server" Font-Names="Verdana" />                
        </td>

And in Javascript:

var inputFile = document.getElementById('ctl00_ContentPlaceHolder1_fuUploadFile');
alert("File size: " + inputFile.size);

Now for some reason, when I try to upload a 50 MB file, inputFile.size returns 20. Can anyone tell why this is? ASP.NET is getting the correct size server side..

@JoeEnos Yes, I tried the latest versions of Chrome and Firefox. — Art F
– Art F, Commented Oct 21, 2013 at 19:15
Not sure if this is your real code, but if so, you should modify it so that you're not hard-coding the client control ID - instead do document.getElementById("<%= fuUploadFile.ClientID %>"), which will render the way you have it. — Joe Enos
– Joe Enos, Commented Oct 21, 2013 at 19:24
@JoeEnos Its not hard coded, but it does use my company's internal Javascript API and I don't want to give anyone a migraine by posting that here.. — Art F
– Art F, Commented Oct 21, 2013 at 19:28

Joe Enos · Accepted Answer · 2013-10-21 19:22:05Z

2

The file's size is found in the element of the files array of the input control.

var numBytes = document.getElementById("fu1").files[0].size;

answered Oct 21, 2013 at 19:22

Joe Enos

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