CHECK BOX Validations

function checkForm()

{

   errorMessage = false

   errorText = " "

   if (document.forms[0].Zip_Postalcode.value == "")

   {

      errorMessage = true

      errorText+="Zip Code n"

   }

   if (errorMessage ==true)

   {

      alert("Please make sure to fill out all required fields. Go back and check: " +  errorText +  "n" ")

      self.location="testjs2.php"

      return false

   }

      if (errorMessage==false)

      {return true}

}