function validate(f) {

	if(isEmpty(f.name)) {

		f.name.focus();
		alert('Please enter your name');
		return false;
	}

	if(emailCheck(f.email)) {

		f.email.focus();
		alert('Your email address is invalid');
		return false;

	}

	if(isEmpty(f.message)) {
		f.message.focus();
		alert('Please enter a message');
		return false;
	}

}

function isEmpty(field) {

	if(field.value.length == 0) {
		return true;
	}
}


function emailCheck(field) {

	var emailExpression = /^[0-9a-zA-Z-\.\_]+@[0-9a-zA-Z-\.]+\.[a-z]{2,3}$/;
	var userInput = field.value;

	if(emailExpression.test(userInput)) {

		return false; // if it passes the test, return false

	} else {

		return true; // else return true
	}

}