Ajax Try Catch Button Example

{!REQUIRESCRIPT("/soap/ajax/32.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/32.0/apex.js")}

if (!window.console) console = {log: function() {}};

/*
sforce.debug.trace=open; //debug helper
sforce.debug.open();
*/

 try{
var result = sforce.apex.execute("DA","Authenticate",{Request:"Attempt Authentication"});
console.log("DEBUG result: " + result);
console.log("DEBUG result.sessionId: " + result.sessionId);

}catch(error) {
     console.log(error);
     alert(error);
  }