When WebWorker file is unaccessible, script should fail silently or post meaningful exception

When WebWorker file is unaccessible, script should either fail silently or post a meaningful message.
Currently, the following exception is thrown:
netscape.javascript.JSException: Error: SYNTAX_ERR: DOM Exception 12 (it can be translated as "The string is invalid for the current operation.")
Script should either fail silently or throw something more specific (having more details).