Question

Is it possible with only one bind to either keyup, keypress or keydown to find out that the field value has been changed?

I mean – some key presses don’t change the value (like pressing left arrow) and some do (like pressing any letter-button or backspace).

So is it possible to know that key press caused the value change having only one binding?

PS: yes, I realize I could save the value somewhere and compare it in the very begin of event handler, but is there a solution without temporary variables?

Answer 1

I don’t think so. I mean, you can map key codes that you assume will be silent, but that map might not be 100% reliable as the input value can change or loose focus depending on how the OS and browser is set up.

Is there a special reason for not detecting change via a variable? It seems like the most reliable thing since this is also exactly what you need to detect:

var input = $('input'),
    val = input.val();
input.keyup(function(e) {
    ​​​​​​​if (val != (val = $(this).val())) {
        console.log('change');
    }
});​

If you don’t want to use stray variables, how about saving it in the data attribute?

$('input').keyup(function(e) {
    ​​​​​​​if ($(this).val() != $(this).data('value')) {
        console.log('change');
    }
    $(this).data('value', $(this).val());
});​

Update based on your comment

You can also use the input event (in modern browsers) to detect change if you don’t care about keys:

$('input').bind('input', function() { 
   console.log('changed');
});

The last option would be to use an interval and keep checking the input field (this might be the most reliable option).