js validation for image ??

[PHPycho]

i am trying to make the javascript validation for images..
For example i tried to upload the file "c:\folder\file.exe"
It should check the extension , if the extension is not image type
should give alert..

what i want?
1> i want to know if there is any function in javascript
that reads the extension of full path like "c:\folder\file.exe"
2> file size
Thanks in advance to all of you !!

[7stud]

1)

var filename = document.getElementById("fileInputID").value;
var ext = filename.substring(filename.lastIndexOf('.') );

2) not possible

[PHPycho]

Pardon again..
is it possible to show the upload preview while uploading with javascript ?

If Yes i am eagerous to know the solution..
Thank you !!