jQuery code triggered twice for bind('keyup change') when pressing key

You have a wrong concept about the onchange event.

It does NOT fire when the element's value changes, instead, it fires only when 2 conditions are met:

• The element blurs (loses focus);
• The element has a different value than when it gained focus.

Note: The above is for inputs of type text. For types checkbox/radio it fires as soon as their checked property changes, and for select elements as soon as its selected option changes.

The onchange event (possibly wrongly) fires when you press Chrome's input type="number" up/down arrows. You should not rely on it, as many other major browsers don't even have an implementation of the number inputs yet and may not follow this behavior.

Instead, as you're using HTML5, you should rely on the oninput HTML5 event, which fires whenever the element's value is updated.

$(function() {
    var count = 0;
    $('#num').on('input', function(e) {
        console.log('update ' + (++count) + ' Value: ' + this.value);    
    });
});​

Fiddle

edit:

For older (and non-HTML5) browsers, you may use the keyup event as a fallback:

$('#num').on('input keyup', function(e) {

The most resilient way to do this for non-HTML5 browsers would be having a setInterval constantly checking if the element's value has changed, as keyup does not trigger if you select some text and drag it into the textbox - you could try .on('input keyup mouseup', but then it wouldn't trigger if the user uses the browser's Edit > Paste menu.

edit2:

If you don't want to use setInterval, you can put a huge events map inside the .on/.bind and check if the value has changed by storing the current value in the .data() of the element:

var count = 0;
$('#num').on('input keyup change', function(e) {
    if (this.value == $(this).data('curr_val'))
        return false;
    $(this).data('curr_val', this.value);

    console.log('update ' + (++count) + ' Value: ' + this.value);
});

Fiddle

I've added the onchange event to the events map, so even if the oninput and onkeyup fails (non-html5 browser using the browser's menu to paste data), the onchange event will still fire when the element loses focus.

Here's the final edit with a commented setInterval and .data() to avoid using globals, so you can choose which of the fallbacks to use:

$(function() {
    var $num = $('#num');
    $num.data('curr_val', $num.val()); //sets initial value

    var count = 0;
    setInterval(function(){
        if ($num.data('curr_val') == $num.val()) //if it still has same value
            return false; //returns false
        $num.data('curr_val', $num.val()); //if val is !=, updates it and
        //do your stuff
        console.log('update ' + (++count) + ' Value: ' + $num.val());
    }, 100); //100 = interval in miliseconds
});

Fiddle