I'm using jquery's function keypress for my input field

Now, let's say that I want to know when the user types a letter, if this is the first character in the field. I now use something like:

element.keypress(function(e){

    //...

    if(elementValue.length()==0){

        //Do something

    }

}

The problem is when the user selects the text that typed and then presses a key (lets say for the character 'A') that replaces it. Then this code returns the length of the old-(soon to be replaced) text.

I know that I could use keyup instead, but I think I need to stay with keypress because I have to do some checks for the pressed physical keys. (this answer really shows the difference between keyup and keypress in this case)

Any suggestions?