nodejs: javascript array issue

Question

I have this node.js app which retrieving subway data from mongodb using mongoose, and after I get the data, I will pass it to sphere-knn to calculate the nearest points. The strange thing happen in var lookup = sphereKnn(d1); if I pass d1 which is hard coded array, the code will work, if I pass the data which is retrieved from mongodb, it won't work at all, and returns empty array as result.

JSON.stringify(data) == JSON.stringify(d1) will print true, Array.isArray will also print true for both d1 and data, console.log will show there are data inside variable data.

I'm confused by the behaviour of the code. I came from .net and new to node.js. do I miss any important concept here?

mrtStop.find({}, {_id:0}, function(err, data){
  if(err){
    return res.json(err);
  }

  // data returned from mongodb, get first one
  data = data.slice(0,1);

  // hard coded data
  var d1 = [{"id":"EW6",
            "name":"EXAMPLE MRT STATION",
            "lat":1.3210355412,
            "lon":103.9129310102,
            "__v":0}];

  console.log(JSON.stringify(data));
  console.log(JSON.stringify(d1));
  // print true
  console.log(JSON.stringify(data) == JSON.stringify(d1));

  // d1 works, but data won't work
  // var lookup = sphereKnn(d1);
  var lookup = sphereKnn(data);

  var points = lookup(req.query.lat, req.query.lon, maxNum);

  res.json(points);
});

OP used == but not ===. == does type conversion. So, i don't know. — Rahat Mahbub
– Rahat Mahbub, Commented May 6, 2016 at 5:48

Medet Tleukabiluly · Accepted Answer · 2016-05-06 06:15:04Z

2

Use Query.lean()

tldr; mongoose returns mongoose-doc object, which has many prototypes, when you lean it, it will return plain js object

//side note: you could also remove `__v` property {_id: 0, __v:0}
mrtStop.find({}, {_id:0}).lean().exec(function(err, data){
  if(err){
    return res.json(err);
  }
  var lookup = sphereKnn(data);
  var points = lookup(req.query.lat, req.query.lon, maxNum);
  res.json(points);
});

answered May 6, 2016 at 6:15

Medet Tleukabiluly

12k3 gold badges38 silver badges78 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

nodejs: javascript array issue

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related