var user_required = new Array('first_name','last_name','amount');
function changeRequired(pay_method){
	if(pay_method=="card"){
		var credit_required = new Array('card_number1','card_number2','card_number3','card_number4','expiration_month','expiration_year');
	}else if(pay_method=="check"){
		var credit_required = new Array('micr_number','drivers_license');
	}
	required = user_required.concat(credit_required);
}

changeRequired('card');