How to disable backspace if anything other than input field is focused on using jquery

Question

How do I disable backspace keystroke if anything other than 2 specific input fields are focused on using jquery?

here is my current code (NOW INCLUDING 2 TEXTBOXES):

Answer 1

Hudson-Peralta's answer worked good for me but I did a small modification since I use many keydown events:

$(document).keydown(function(e){ 
            var elid = $(document.activeElement).is("input:focus"); 
            if(e.keyCode === 8 && !elid){ 
               e.preventDefault(); 
            }; 
        });