JavaScript/Working with files
With pure HTML4 and pure JavaScript, there's really only one thing you can do with the users files:
The server sends a Web page that includes a form something like this:[1]
<form action="/upload_handler" method="post">
<input type="file" />
</form>
and then, the browser allows the user to select one file, and the browser uploads it -- without any JavaScript on the client being able to see any of that data or cancel the transmission or even show a progress bar.
If you want JavaScript to know anything about the file before it is transmitted (for example, to immediately cancel the transmission of a large file rather than wait an hour for the file to be transmitted, then tell the user "File too large"; or to show a progress bar), you'll have to use something other than pure JavaScript on pure HTML4.
Some popular options are:[2][3][4][5]
- use a modern Web browser that supports the HTML5 File API.
- use Flash (perhaps a tiny flash utility like Gmail uses to draw a little progress bar)
- use a Java applet
- use an ActiveX control