Question

In html5 fields can be valid. (for example an type="email" has to follow the email convention etc).

Using css you can select valid fields with the psuedo-element:
input:valid.

Is it possible to trigger an event when the input becomes valid?

Answer 1

Use the checkValidity() method on the input’s DOM element you want to check.

function isValidInput (input) {
    return $(input)[0].checkValidity();
}

Then you can run that function on whatever event, like blur or keyup or a button.

Demo: http://jsfiddle.net/nSLQb/1/