title: How to tell whether a Javascript error is 'blocking'?
body: <p>Is there such a thing as blocking vs non blocking Javascript errors?</p>
  
  <p>What I mean is that I've seen my site report some errors, but the process involved still completes successfully (as far as I can tell). These errors include:
  TypeError: undefined is not an object (evaluating 'e.nodeName.toLowerCase')
  TypeError: e.nodeName is undefined
  (these are always from my general JQuery library file)</p>
  
  <p>These are what I mean by 'non-blocking' errors, since the scripts involved seem to complete successfully.</p>
  
  <p>If there is such a thing as blocking v non-blocking, what is the correct terminology for it, and how can I tell the difference between the 2 (eg so that I can prioritise investigating blocking errors)?</p>
  
  <p>Thanks</p>