quick hahahahahahahahahaha question

<!--

//define the function

function checkForm(formName) {

//state that contactinfo is each feild on the form

for( var contactinfo = 0; contactinfo < document.forms[formName].elements.length; contactinfo++)

//if any fields are blank

if ( document.forms[formName].elements[contactinfo].value hahahaha '' )
{
document.forms[formName].elements[contactinfo].focus();

//alert the user which fields they did not fill out

alert( 'Please fill in your ' + document.forms[formName].elements[contactinfo].name );
}


}
//-->


im using this like this >>

form name="form" action="mailto:[email protected]" method="post" OnSubmit=checkForm("form")









so - when i click submit it goes through and it alerts what fields are missing input but what do i need to do to make it so if the alert comes up it stops and doesn't submit!?