ideas regarding preventing form submission when there is JS error

Below is a snippet of the code I am using to validate a form.

//this function validates the form
function Validate() {
	document.getElementById('submit_form').value="Sending...";
	document.getElementById('submit_form').disabled=true;

	var errfound = "false";
	var errmsg = "";

	var valfname = document.regform.fname.value;

	
	if (valfname.length < 1) {
		errfound = "true";
		errmsg = errmsg + "Please enter a First Name. \n";
	}


	if (errfound == "true") {
		alert(errmsg);
	    document.getElementById('submit_form').disabled=false;
	    document.getElementById('submit_form').value="Submit";
		return(false);
	} else {
		return(true);
	}
	return(false);
}//end function

Is there a way to stop the form from submitting (returning "true") if there is an error in the Javascript?

Normally, I include the form action in the JS - but I am working a team who keeps reversing my code and frankly I just dont want to deal with their unbending ideology. However, I don't want my forms to submit without passing the validation script. (Forms using this script will submit if there is a Javascript error).