submitting a form without a submit button

The main idea behind this is to use Java script submit() function inorder to submit the form without explicitly clicking any submit button.

You can attach the document.formname.submit() method to onclick,
onchange events of different inputs and perform the form submission.

(or)

you can even built a timer function where you can automatically submit the
form after xx seconds once the loading is done (can be seen in online test sites).