How to catch parser errors?

How can I catch parser errors numbers?

I currently use something like this:

try {
   someElement.innerHTML = foopydoopy;
} catch(ex) {
  dump(ex);
  >>> [Exception... "An invalid or illegal string was specified"  code: "
12" nsresult: "0x8053000c (NS_ERROR_DOM_SYNTAX_ERR)"  location: xxx 
Line: nnn"] <<<
}

but I don't want to lookup the error code in that string, so how can I 
solve this problem?

Thanks,
Michael