Is there a way to determine if a JS event was fired programmatically or by an actual interaction?

Say I programmatically set focus on a textarea with a simple document.getElementById('myTextArea').focus();. On that textarea I have an onFocus event:

document.getElementsByName('myTextArea')[0].onFocus = function () {
    alert('I’m focused!');
};

I only want that onFocus to be fired when the user actually focuses on the textarea and not when I set focus programmatically.

Is there a way in the onFocus to tell if the event was triggered by code or by a human, without passing in a parameter of my own?