he everyone please i want to know how to submit a form using ajax every 5 minutes without reloading page

i have a huge form for exams and i need to submit the form without the need to wait until pressing submit because the user may wait to think about the answer a very long time..

so i want to submit the form and at the same time i cant reload the page as it is in normal submit form..

so how i can submit form in the background without letting the user knows that the form is submitted???