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

To detect email for example, I tried "on change" and a mutation observer, neither worked. setInterval works well with LinkedIn auto-fill (not revealing all my code, but you get the idea) and it plays nice with the backend if you add extra conditions here to slow down the AJAX. And if there's no change in the form field, like they're not typing to edit their email, the lastEmail prevents pointless AJAX pings.

// lastEmail needs scope outside of setInterval for persistence.
var lastEmail = 'nobody';
window.setInterval(function() { // Auto-fill detection is hard.
    var theEmail = $("#email-input").val();
    if (
        ( theEmail.includes("@") ) &&
        ( theEmail != lastEmail )
    ) {
        lastEmail = theEmail;
        // Do some AJAX
    }
}, 1000); // Check the field every 1 second