//checks email address is valid
function isEmailAddress (string) {
  var addressPattern = 
    /^\w+((-\w+)|(\.\w+))*\@[A-Za-z0-9]+((\.|-)[A-Za-z0-9]+)*\.[A-Za-z0-9]+$/;
  return addressPattern.test(string);
}
//checks form elements contain data
function validate() {
	if (document.forms[0].name){
		var f = document.forms[0].name;
		if (f.value == ""){
			alert("Please enter your name.");
			f.focus();
			return false;
		} 
	}
	if (document.forms[0].phone){ 
		var p = document.forms[0].phone;
		if (p.value == ""){
			alert("Please enter a phone number.");
			p.focus();
			return false;
		}
	} 
	if (document.forms[0].email){
		var e = document.forms[0].email;
		if (e.value == ""){
			alert("Please enter an email address.");
			e.focus();
			return false;
		}
		if (!isEmailAddress(e.value)) {
			alert("Please enter a valid email address.");
			e.focus();
			return false;
		}
	} 
	if (document.forms[0].message){ 
		var p = document.forms[0].message;
		if (p.value == ""){
			alert("Please enter your message.");
			p.focus();
			return false;
		}
	} 
}