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      function zipChanged(zip) {
          if(zip.length != 5) {
              clearCityAndStateFields();
          }
          else {
              new Ajax.Request(
               "zipChanged.ajax",   // URL
                 {     method: "get", // HTTP method
                   parameters: "zip=" + zip, // Request params
                   onComplete: processZipCodeSelection, // callback
                 });
          }
      }

• Although simple, it still requires server-side logic in the form of a servlet.
• Ajax servlets are middlemen that generally call JavaBean methods.