Possible binding loss in Expressjs?

Question

Possible binding loss in Expressjs?

so I am running into what I think is a binding issue, caused by connect-mongo or expressjs Here is the code:

  //Error
  app.use(function(err, req, res, next) {

        if (err instanceof noData) {
            res.send(err, 404);
        } else {
            next(err);
        }
  });

My custom error handler

function noData(err){
  this.code = 0;
  this.msg = err;
  console.log(Error);
  Error.call(this, {code:0, msg:err});
  Error.captureStackTrace(this, arguments.callee);
};
noData.prototype.__proto__ = Error.prototype;

Throwing error here:

  err = true;
  //if(err) throw new noData('No Password');
  //Get user from database
  db.collection('users').find({}, {limit:1}).toArray(function(err, result) {
    if(err) throw new noData('No Data');             
  });

The first error throws correctly, but the second one but the second one throws a general nodejs error.

throw e; // process.nextTick error, or 'error' event on first tick

What am i doing wrong here? Is connect-mongo causing it to lose binding somehow? Any thoughts are greatly appreciated.

node.js
mongodb
express

Answer 1

The problem doesn't lie in express or connect-mongo, the callback is in a different scope. To resolve this simply add a (this) to the end of the call.

  //Get user from database
  db.collection('users').find({}, {limit:1}).toArray(function(err, result) {
    if(err) throw new noData('No Data');             
  }(this));

Now node knows about my custom error. (hallelujah) This essentially an iife which allows me to pass in a param.