Detecting Browser Autofill

Question

How do you tell if a browser has auto filled a text-box? Especially with username & password boxes that autofill around page load.

My first question is when does

Answer 1

If you only want to detect whether auto-fill has been used or not, rather than detecting exactly when and to which field auto-fill has been used, you can simply add a hidden element that will be auto-filled and then check whether this contains any value. I understand that this may not be what many people are interested in. Set the input field with a negative tabIndex and with absolute coordinates well off the screen. It's important that the input is part of the same form as the rest of the input. You must use a name that will be picked up by Auto-fill (ex. "secondname").

var autofilldetect = document.createElement('input');
autofilldetect.style.position = 'absolute';
autofilldetect.style.top = '-100em';
autofilldetect.style.left = '-100em';
autofilldetect.type = 'text';
autofilldetect.name = 'secondname';
autofilldetect.tabIndex = '-1';

Append this input to the form and check its value on form submit.