Validation of mandatory questions does not work when adding code

I have a question about the code 

window.location.href = "REDIRECT URL GOES HERE";

if I have mandatory questions in the form, with this code if I press send without answering all the survey questions, the validation of mandatory questions is passed. 
Is there any condition where it says that, if the error is active, do not go to the thank you page until all the required questions are answered?

Thanks!