fint the height of a file before the upload

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?

It's not possible. JavaScript has no way of accessing the file size.

You must check it after it has been submitted.