// JavaScript Document
function formvalidator_contactus()
{
	// Make quick references to our fields
	var name = document.getElementById('name');
	var email = document.getElementById('email');
	var mobile= document.getElementById('mobile');
	var message = document.getElementById('message');
	
	if(isEmpty(name, "Enter Only Letters for Your Name")){<!--1
	if(emailValidator(email, "Enter Valid Email-Address")){<!--2
	if(isNumeric(mobile, "Enter Valid Mobile Number")){<!--3
	if(isEmpty(message,"Enter Your Feedback / Comments")){<!--4
			return true;								
		
		} <!--1
		}<!--2
		}<!--3
	    }<!--4
		
	return false;
}

<!-- is empty
function isEmpty(elem, helperMsg){
	if(elem.value.length == 0){
		alert(helperMsg);
		elem.focus(); // set the focus to this input
		return false;
	}
	return true;
}
<!---------- Number validation
function isNumeric(elem, helperMsg){
	var numericExpression = /^[0-9]+$/;
	if(elem.value.match(numericExpression)){
		return true;
	}else{
		alert(helperMsg);
		elem.focus();
		return false;
	}
}

<!----------------------- Email Validation
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;
	}
}