var fieldToFocus;
function computeForm(form) {
  error = false;


if (error == false && isBlank(form.yName,"Your Name"))
  { 
      error = true;                                       
  }

if (error == false && !(validEmail(form.yEmail)))
  {
	error = true;
  }

if (error == false && isBlank(form.Question,"Your Note"))
  { 
      error = true;                                       
  }


  if (error)
     return false;
    else
     return true;
}


<!-- To check if the input is blank-->
	function isBlank(field,msg)
	{
		if (field.value == "") {
    			alert ("You Must Enter "+msg);
    			field.focus();
    			field.select();
    			return true ;
 		} 
		else 
		{
   	 		return false ;
 		}
	}

<!--To check for valid Email address-->
function validEmail(eAddr) 
{ 
   var ndxAt = ndxDot = 0;

   ndxAt  = eAddr.value.indexOf("@");
   ndxDot = eAddr.value.indexOf(".");

   if ( (ndxDot < 0) || (ndxAt < 0) || (ndxDot < ndxAt) || ((ndxDot - 3) <= ndxAt) || (eAddr.length < (ndxDot + 4)) )
   {
      alert("Your email is invalid");  
      eAddr.focus();
      eAddr.select();
      return false;  
    }
    else
    {
      return true;
    }                      
}