For me, this is only ok if at the top of the form there is big easy to read text that says any data typed in the form is saved immediately prior to the user hit

For me, this is only ok if at the top of the form there is big easy to read text that says any data typed in the form is saved immediately prior to the user hitting submit. Anything else is a dark pattern. Let's not kid ourselves. We know most users naively think the data is just on their screen and nowhere else until they hit submit. If we write code to circumvent that expectation we know it is a deception. After all, the default behavior is that the form data is not available early. The programmer has to explicitly do something to counter the default.