Asynchrously load NPM module

Question

I'm trying to create a module that connects to my Database (couchDB using Cradle). In the end, the module exports the 'db' variable.

Here is the code:

var cradle = require('cradle'),
config = require('./config.js');

var db = new(cradle.Connection)(config.couchURL, config.couchPort, {
    auth: {
        username: config.couchUsername,
        password: config.couchPassword
    },
    cache: true,
    retries: 3,
    retryTimeout: 30 * 1000
}).database('goblin'); //database name



//Check if DB exists
db.exists(function (err, exists) {
    if (err && exists) {
        console.log("There has been an error finding your CouchDB. Please make sure you have it installed and properly pointed to in '/lib/config.js'.");
        console.log(err);
        process.exit();
    } else if (!exists) {
        db.create();
        console.log("Welcome! New database created.");
    } else {
        console.log("Talking to CouchDB at " + config.couchURL + " on port " + config.couchPort);
    }

});

module.exports = db;

The problem is that the db.exists call is async, and if it doesn't exist I think the variable exports the variable before it's done, effecting the rest of the system.

It's being included in the executed node page the normal way:

var db = require('./couchdb.js');

Is there a way to prevent this from happening, or any best practices to tackle a problem like this without having a giant nested callback?

For reference, you can see the entire application right here (https://github.com/maned/goblin) , and the bug referenced for the project here (https://github.com/maned/goblin/issues/36).

Answer 1

Embrace the async style. Instead of exporting db from the module, export an async function like this:

module.exports = {
  getDb: function(callback) {
    db.exists(function(err, exists) {
      if (exists && !err) {callback(db);} else { /* complain */ }
    });
  }
};

Now the application can just require('mymodule').getDb(appReady) where appReady accepts a db object that is known to be valid and usable.