Question

According to the official documentation, this event is:

Triggered when the field is blurred, if the value has changed;

Now, how does it know if the value has changed? Is it stored somewhere? And the reason I ask: can I replicate that behaviour?

Thanks

Answer 1

This is resolved by the browser. You can also trigger for values changed on text inputs by attaching a handler to the onchange event:

<input onchange="alert('value changed!');" />

And also in Javascript:

document.getElementById("my_text_input").onchange = function(){
    alert("value changed!");
}

Of course you can replicate this behaviour. You can try it yourself here.

[Edit]
You have the onblur event, which fires every time the user leaves the control.
You could keep track of the input value, or set a flag to be accesible for both change and blur events:

(function(){
    var changed = false;

    document.getElementById("my_text_input").onchange = function(){
        changed = true;
    }
    document.getElementById("my_text_input").onblur = function(){
        if (!changed) {
            //Your logic here
        }
        changed = false; //set it back to false for next loss of focus
    }
})();