function validate() {
  var f_name = document.getElementById('f_name');
  var l_name = document.getElementById('l_name');
  var email = document.getElementById('email');
  var subject = document.getElementById('subject');
  var message = document.getElementById('message');
  
  if(isAlphabet(f_name, "Please enter first name.")) {
  	if(isAlphabet(l_name, "Please enter last name.")) {
       if(emailValidator(email, "Please enter email address.")) {
	       if(isAlphabet(subject, "Please enter a message subject.")){
		       if(isAlphabet(message, "Please enter a message.")) {
			       return true;
		       }
	       }
       }
    }
  }
  return false;
}

function isAlphabet(elem, helperMsg){
	var alphaExp = /^[a-z A-Z]+$/;
	if(elem.value.match(alphaExp)){
		return true;
	}else{
		alert(helperMsg);
		elem.focus();
		return false;
	}
}

function emailValidator(elem, helperMsg){
	var emailExp = /^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/;
	if(elem.value.match(emailExp)){
		return true;
	}else{
		alert(helperMsg);
		elem.focus();
		return false;
	}
}

function isAlphanumeric(elem, helperMsg){
    var alphaExp = /^[0-9a-zA-Z ]+$/;
    if(elem.value.match(alphaExp)){
        return true;
    }else{
        alert(helperMsg);
        elem.focus();
        return false;
    }
}