How can I get a file's upload size using simple Javascript?

Question

I have upload file functionality on one of the page. I check for the extension of the file using JavaScript. Now i want to restrict the user from uploading file greater than 1 MB. Is there any way i can check the file upload size using JavaScript.

My code currently look like this:

<script language="JavaScript">
function validate() {
   var filename = document.getElementById("txtChooseFile").value;
   var ext = getExt(filename);
   if(ext == "txt" || ext == "csv")
      return true;
   alert("Please upload Text files only.");
   return false;
}

function getExt(filename) {
   var dot_pos = filename.lastIndexOf(".");
   if(dot_pos == -1)
      return "";
   return filename.substr(dot_pos+1).toLowerCase();
}
</script>

Answer 1

Other that aquiring the filename there is no way for you to find out any other details about the file in javascript including its size.

Instead you should configure server-side script to block an oversized upload.

Answer 2

It might be possible using a lot of browser-specific code. Take a look at the source of TiddlyWiki, which manages to save itself on the user's hard drive by hooking into Windows Scripting Host (IE), XPCOM (Mozilla), etc.

Answer 3

I don't think there is any way of doing that with plain JS from a web page.
With a browser extension maybe, but from a page javascript cannot access the filesystem for security reasons.

Flash and Java should have similar restrictions, but maybe they are a bit less strict.

Answer 4

not possible. would be a major security concern to allow client side scripts to run that can read file info from and end users hard drive.

Answer 5

See http://www.w3.org/TR/FileAPI/. It is supported by Firefox 3.6; I don't know about any other browsers.

Within the onchange event of a <input id="fileInput" type="file" /> simply:

var fi = document.getElementById('fileInput');
alert(fi.files[0].size); // maybe fileSize, I forget

You can also return the contents of the file as a string, and so forth. But again, this may only work with Firefox 3.6.