detecting page change

I wrote a script to brute force a solution to a quiz on a google forms page There is a text field and a button
Entering a guess in the field and pressing the button results in either a text message that the solution is wrong or a new page is loaded saying the answer is correct

I successfully wrote a simple loop that changes the text of the field and presses the button

1. How can I detect the page change after the button is pressed? (when the guess is correct)
2. When I just looped through the numbers 000-999 the solution page did not load (I was expecting the script to fail at the next number since the input field is not present in the solution page). However, when I debugged the script, single-stepping the solution caused the browser to load the solution page. Do I need to add a delay (sleep) after the button click?