setting the value of a file object

swarnap · November 4th, 2006, 04:03 AM

I have a control on me screen of type <FILE>. I want to set some value to that object from the database. I tried the following code using html.

<html >
<head>
<script type="text/javascript">
  function fun()
  {
    document.getElementById('j').value="hi"
    alert(document.getElementById('j').value);
  }
</script>
</head>

<body>
<input type="file" value="hello" id="j" />
<input type="button" onclick="alert(document.getElementById('j').value) ;"
<input type="button" onclick="fun();"
</body>
</html>
but none of the above showed proper values for alert. it was showing null.

If I'm entering some values into the file field manalyy then proper alert is coming.
If I change the file type to text, then it is setting the value in the textfield with the value in the value attribute.

So my question is how to I set the value into the <FILE> type through the code implicitly.

meow · November 4th, 2006, 04:32 AM

You would probably get a better answer in the JavaScript forum, http://p2p.wrox.com/javascript-85/ , but I don't think you can do what you want, not reliably anyway. See http://www.cs.tut.fi/~jkorpela/forms/file.html#value .

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richard.york · November 6th, 2006, 10:04 AM

You can set the value of a file input if you have elevated security settings (as is the case on an intranet).

If this isn't an intranet site, you'll have to get the user to trust your site to do that. In IE, that means granting your site elevated privileges.

I'm not sure how it's done in IE from the standpoint of code, it may just be a matter of trusting the site. In Firefox, you have to have a signed script. Without a signed script, you can enable a special security dialogue, which once allowed will allow you to set the value of file objects.

To do that without a signed script, following is the process:

Add the following to prefs.js (located in Firefox profile folder)

Code:

user_pref("signed.applets.codebase_principal_support", true);

Then your script must ask the user for permission, I think both of these are required.

Code:

        try
        {
            netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
        }
        catch($err)
        {
            var $privileges = false;
            alert('Error: Unable to perform file upload. App was denied elevated privileges to do so.');
        }

AND

Code:

        try
        {
            netscape.security.PrivilegeManager.enablePrivilege('UniversalFileRead');
        }
        catch($err)
        {
            var $privileges = false;
            alert('Error: Unable to perform file upload. App was denied elevated privileges to do so.');
        }

This technique enables the security prompt on your computer alone, which is good for testing. To get the prompt on everyone else's, you must have a signed script, or you must manually install that line in their prefs.js file.

So, as you can see there are a lot of security hurdles, and rightly so. If you could just arbitrarily set the value of the file upload, you could upload files from the user's computer without their knowing, and that would be bad.

HTH!

Regards,
Rich

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joefawcett · November 6th, 2006, 11:13 AM

IE will let you set the value in code but you won't be able to upload the file when the form is posted.

--

Joe (Microsoft MVP - XML)