node.js: Throwing error and it's not being caught

Question

I have an API using swagger integrated with express on node.js and a resource defined as below. A swagger error thrown in the check for (!req.params.id), is caught by swagger's default error handler. An error thrown in the callback from the mongoDB delete call is NOT caught, giving me the error below. The error looks like it has to do with the scope/order of the callback function, and as somebody new to node.js I was hoping to get advice on how to do this properly, maintaining asynchronicity. -thanks

events.js:74 throw TypeError('Uncaught, unspecified "error" event.'); ^ TypeError: Uncaught, unspecified "error" event.

exports.remove = {
    'spec' : {
      "collapsed...for...brevity..." : "...",
      "params" : [ {
        "paramType" : "path",
        "name" : "id",
        "collapsed...for...brevity..." : "...",
      }],
      "errorResponses" : [ swe.notFound('id'), swe.invalid('id') ],
      "nickname" : "remove"
    },
    'action' : function(req, res) {

      if (!req.params.id) {
        throw swe.invalid('id');   // THIS ERROR IS CAUGHT
      }

      req.coll.remove({_id : req.coll.id(req.params.id)}, function(e, result) {
        if (e) {
          throw swe.invalid('collection');   // THIS ERROR IS NOT CAUGHT
        }

        res.send({msg : 'success'});
      });
    }
  };

Answer 1

Exceptions thrown within an async callback go to the caller of the callback, not your surrounding code. So it's the req.coll.remove code that receives the exception (which isn't handling it) and that crashes your app.

Instead, you need to have your remove action function accept a callback parameter that it can use to communicate errors back to the caller.

This is why exceptions are rarely used in node.js code and callbacks are the standard.