jQuery Missing Parenthesis on function causes Cross-Orgin Error

Question

I forgot () on the jQuery val function but received a strange error and am wondering what the cause of that was.

I had the following code:

$('#element').on('focusout', function() {
    $.post("/ajax", 
        {
            email: $('#email').val,
        }
    );
});

and received:

Uncaught DOMException: Blocked a frame with origin "https://example.com" from accessing a cross-origin frame.

It seems like my syntax error must have been executing something else.

This is a static HTML page, no iframe, frame or any content hosted on another domain/subdomain.