Node.js and mongodb: TypeError: Cannot read property 'findAll' of undefined

Question

I am following this Node.js and mongodb tutorial with javascript (https://www.raywenderlich.com/2663-how-to-write-a-simple-node-js-mongodb-web-service-for-an-ios-app).

I am getting an error when I run node and mongodb from terminal then go to http://localhost:3000/items. The error appears to be in this block of code:

app.get('/:collection', function(req, res) { //A
   var params = req.params; //B
   collectionDriver.findAll(req.params.collection, function(error, objs) { //C
          if (error) { res.send(400, error); } //D
          else {
              if (req.accepts('html')) { //E
                  res.render('data',{objects: objs, collection: req.params.collection}); //F
              } else {
              res.set('Content-Type','application/json'); //G
                  res.send(200, objs); //H
              }
         }
    });
});

In the code above this, I set the collectiondriver database:

var collectionDriver;
var mongoClient = new MongoClient(new Server(mongoHost, mongoPort)); //B
mongoClient.open(function(err, mongoClient) { //C
  if (!mongoClient) {
      console.error("Error! Exiting... Must start MongoDB first");
      process.exit(1); //D
  }
  var db = mongoClient.db("MyDatabase");  //E
  collectionDriver = new CollectionDriver(db); //F
});

The error when I go to localhost:3000/items is:

TypeError: Cannot read property 'findAll' of undefined
    at /Users/username/Documents/NodeTutorial/index.js:32:21
    at Layer.handle [as handle_request] (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/layer.js:95:5)
    at next (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/route.js:137:13)
    at Route.dispatch (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/route.js:112:3)
    at Layer.handle [as handle_request] (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/layer.js:95:5)
    at /Users/username/Documents/NodeTutorial/node_modules/express/lib/router/index.js:281:22
    at param (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/index.js:354:14)
    at param (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/index.js:365:14)
    at Function.process_params (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/index.js:410:3)
    at next (/Users/username/Documents/NodeTutorial/node_modules/express/lib/router/index.js:275:10)

Line 32 in index.js starts with "collectionDriver.findAll". What is the reason findAll() is undefined?

The expected output of the page in localhost:3000/items should look like the following as explained in the tutorial:

Can anyone please tell me what is wrong? I am using mongodb version 1.3.23 (like the tutorial uses)

Answer 1

Node js runs asynchronously. In your case, I think the "collectionDriver" is not getting initialized before you use it. Try to use promises to make them synchronized. Make sure your "collectionDriver" is initialized before you call .findAll(...).

I hope my answer helps.