Test the way that various errors are reported in user scripts.

errorizer.user.js

// ==UserScript==
// @name           Error-izer
// @namespace      https://github.com/arantius
// @description    Cause all sorts of different errors.  One at a time.
// @include        http*
// @unwrap
// ==/UserScript==

var errorId = GM_getValue('errorId', 1);
errorId++;
GM_setValue('errorId', errorId);

function makeProblems() {
dump('Triggerring error (' + errorId + '), kind: ');
switch (errorId) {
case 1:
  dump('null dereference.\n');
  null.property;
  break;
case 2:
  dump('call null.\n');
  null();
  break;
case 3:
  dump('call undefined.\n');
  undefined();
  break;
case 4:
  //dump('document.write "Security error" (FF3).\n');
  //document.write('');
  break;
case 5:
  dump('thrown.\n');
  throw new Error('foo');
  break;
case 6:
  dump('override global.\n');
  eval('var sidebar;');
  break;
case 7:
  dump('syntax.\n');
  eval('for(1;2;)');
  break;
default:
  dump('unknown.  Resetting for next run.\n');
  GM_setValue('errorId', 0);
  break;
}
}

setTimeout(makeProblems, 0);
// This one causes a compile time error, regardless of position, when @unwrap:
//var sidebar;

// Syntax errors also happen at compile time:
//for (a;b)