Customize Apex Exception Messages from Javascript Buttons

Question

My application has javascript button that call Apex code. Exceptions from web services are sometimes thrown and the user is shown a detailed exception message like this:

A problem with the OnClick JavaScript for this button or link was encountered:
{faultcode:'soapenv:Client', faultstring:'HttpException: Example Error Message
Class.BananaWebService.fetchBanana: line 22, column 1', }

Is there a simple way to create friendly error messages for my users when exceptions are thrown like this:

Example Error Message

Exception Class

public class HttpException extends Exception{}

Web Service Class

@RestResource(urlMapping='/BananaWebService/*')
global class BananaWebService {
  webservice static void fetchBanana(Id accountId) {
     throw new HttpException('Example Error Message');
  }
}

Javascript code

{!REQUIRESCRIPT("/soap/ajax/28.0/connection.js")} 
{!REQUIRESCRIPT("/soap/ajax/28.0/apex.js")} 

var accountId = "{!Account.Id}";
sforce.apex.execute("BananaWebService","fetchBanana", { accountId: accountId }); 
window.location.reload();

Answer 1

Use your own try-catch block inside your function:

{!REQUIRESCRIPT("/soap/ajax/28.0/connection.js")} 
{!REQUIRESCRIPT("/soap/ajax/28.0/apex.js")} 
try {
var accountId = "{!Account.Id}";
sforce.apex.execute("BananaWebService","fetchBanana", { accountId: accountId }); 
window.location.reload();
} catch(e) { alert("I'm sorry. I can't let you do that, Dave. Here's why: \n\n"+(e.message||e)); }

Feel free to customize the error message as you like. You might need to adjust the value for "e", as well.