<FORM onReset="handler-statements" a definition of the handler ...attributes... other attributes here > form.onreset a reference to the handler form.onreset(); an explicit invocation of the handler
onreset() is an event handler of the Form object, and is invoked when the form is reset, either through the Form.reset() method or when the user clicks on a Reset button.
If the onreset() handler returns false, then the elements of the form will not be reset.
You could use the following event-handler to ask the user to confirm that they really want to reset the form:
<FORM ... onReset="return confirm('Really erase all entered data?')" >