fint the height of a file before the upload

[noamway]

I give user the option to upload a file
to my site. The weight limit is 750KB.

I want the JavaScript code check before the upload
if the weight of the file is OK (small than 750KB).

I found a way to check picture files, but when the user upload music Or movie file the check don't work.

someone can give me idea how to do this?