This simple script will prevent javascript errors from being displayed in your visitor's browser

<script type="text/javascript">
function noError(){return true;}
window.onerror = noError;
</script>

Or jQuery:

$(window).error(function(){
  return true;
});

The functionality is very simple: create a function that always returns true, and then whenever an error occurs, call this function (returning true and suppressing the error).

Shamefully, this script is only tested in IE.