prevent_backspace_history

// via UX-SE
// http://ux.stackexchange.com/a/54443

var hasfocus = 'false';

// when focus happens, set a variable
$(document).on('focusin','input, textarea',function() {
    hasfocus = 'true';
    });

// unset when focus is not happening    
$(document).on('focusout','input, textarea',function() {
    hasfocus = 'false';
    });

// if not in a form field, stop backspace and delete default action
$(document).keypress(function (e) {
    if(e.which == 8 || e.which == 46) {
        if(hasfocus == 'false') {
            e.preventDefault();
           }
       }
    });