Building a web app with node js

NodeJS is an event driven javascript framework that makes writing asynchronous code a piece of cake! For small apps and a limited user base, this is almost magical - the code can be churned out fast, it is clean and it is perfectly unit testable. The purpose of this blog is not to sell node js though, we’ll instead look at how an application could be built easily.

The applications I work on are primarily client-server, like web apps, or mobile apps with a backend. So here’s what my toolkit with node js looks like:

Express JS: Sinatra like web framework that gives basic structure to the web app
Sequelize JS: ORM framework
Require JS: for modularization
Node DB Migrate module: just like rails db migrations
Mocha JS: For unit tests
Chai JS: For test assertions
Crypto: For encryptions
Angular JS: For the front end
MySQL: database

Lets keep the front end out of scope for this article and only focus on getting an app that can serve JSON over REST.

Setting up the environment

Install nodejs
Next, we need expressjs

Run the following

     npm install -g express
     # create the app now. we'll call it 'myapp'
     express myapp
     cd myapp
     node app.js

You should now see something like this “Express server listening on port 3000”
Yay! You now have a basic Express JS app running!

Configuring the app

The ExpressJS guide is a pretty good resource for getting started, so I would recommend that you read through it.

Next, add the following in package.json under dependencies:

{
  "mysql": "*",
  "supervisor": "*",
  "db-migrate": "*",
  "sequelize": "*",
  "requireindex": "*",
  "mocha": "*",
  "crypto": "*",
  "chai": "*"
}

Save package.json and run “npm install”
Supervisor module is a great module for development environments and it auto reloads the app on change, so you dont have to restart your node server every time. To run the app using supervisor, just use “supervisor app.js”
Requireindex is a nice module that helps get all objects from a directory into a single object, without adding a “require” for each file

Add the error handler in app.js (as described in expressjs guide)

app.use(function(err, req, res, next){
  console.error(err.stack);
  res.send(500, 'Something broke!');
});

Run the app again and access using http://localhost:3000.

Adding database support

Install mysql
We already have the node module included in package.json (mysql), so the app is now ready to start talking to the database
We’ll use node db migrate module to set up the database.

Create a file database.json under myapp. The contents should look as follows:

    {
 "dev": {
   "driver": "mysql",
   "user": "root",
   "database": "myapp"
 },

 "test": {
   "driver": "mysql",
   "user": "root",
   "database": "myapp_test"
 },

 "production": {
   "driver": "mysql",
   "user": "root",
   "database": "myapp"
 }
    }

Create a db.js in the myapp directory with the following contents:

var express = require('express'),
    Sequelize = require("sequelize");

var app = express();
var env = app.get('env') == 'development' ? 'dev' : app.get('env');

// db config
var fs = require('fs');
var dbConfigFile = __dirname + '/database.json';
var data = fs.readFileSync(dbConfigFile, 'utf8');

var dbConfig = JSON.parse(data)[env];
var password = dbConfig.password ? dbConfig.password : null;
var sequelize = new Sequelize(dbConfig.database, dbConfig.user, password, { logging: true });

exports.sequelize = sequelize

The above uses the same file (database.json) as used by db-migrate module so all your configuration stays at one place. It also initializes our ORM framework viz. sequelizejs.
To use this, just add require('db.js') as required and get sequelize.

Configure unit tests

Modify your package.json and add the following under “scripts”:

"pretest": "db-migrate up -m ./migrations --config ./database.json -e test",
"test": "NODE_ENV=test mocha test test/*/**"

The above will ensure that your db migrations are run automatically when you run the tests, and also that you don’t have to remember longish commands for recursively running tests in sub directories.

Add a basic test case under “test” directory.

var expect = require('chai').expect,
should = require('chai').should();
var db = require("../db.js").sequelize;
var DataTypes = require("sequelize");
var assert = require("assert")
describe('DB', function(){
    it('should check db connection', function(done){
        db
        .query("select count(1) from users")
        .success(function(o){
            expect(o.length).to.not.equal(0);
            done();
        }).error(function(error) {
            done();
        });
  })
})

Prepare for test data - create a file _setup.js under tests and put the following:

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

var testData = [
"INSERT INTO users (name) VALUES ('test user');",
"INSERT INTO users (name) VALUES ('test user 2');"
];

// now run the test data
testData.forEach(function(sql){
    db.query(sql).success(function(){ }).error(function(e){ console.log(e); });
});

console.log(">>>> starting tests...");

The SQLs above are obviously just indicative and you’ll have to add your SQLs as needed.
Run npm test to execute the tests!

Build a model

Start creating your db migrations (like db-migrate create users) ! They will be stored under myapp/migrations directory.
Run the following:
```
db-migrate create users
```

Now open the migration that has been created under migrations directory and add table definition, e.g.

var dbm = require('db-migrate');
var type = dbm.dataType;

exports.up = function(db, callback) {
    db.createTable('users', {
        id: { type: 'int', primaryKey: true, autoIncrement: true },
        name: 'string'
      }, callback);
};

exports.down = function(db, callback) {
    db.dropTable('users', callback);
};

Run the migrations to create users table.
Now create a directory called “models” under myapp. This is where we’ll put our models.

Under models, create users.js with the following contents (or similar)

var db = require("../db.js").sequelize;
var crypto = require('crypto');
var DataTypes = require("sequelize");

var User = function(name, username, password) {
  this.name = name,
  this.user_name = username,
  this.password = password
};

var users_table = db.define('users', {
     name: DataTypes.STRING,
     user_name: DataTypes.STRING,
     password: DataTypes.STRING
   }, {
     timestamps: false,
     underscored: true
   });

User.prototype.save=function(onSuccess, onError) {
   var shasum = crypto.createHash('sha1');
   shasum.update(this.password);
   this.password = shasum.digest('hex');

   users_table.build(this).save().success(onSuccess).error(onError);
};

User.find=function(username, password, onSuccess, onError) {
   users_table.find({ where: {user_name: username, password: password}, attributes: ['id', 'name', 'user_name'] }).success(onSuccess).error(onError);
};

User.lookup=function(name, onSuccess, onError) {
   users_table.findAll( { where : [ "name like ?", '%' + name + '%' ] } ).success(onSuccess).error(onError);
};

exports.get=User;
exports.table=users_table;

As a reminder, we use sequelizejs for ORM and crypto for encryptions above.
To use this model, all we now need is to create an object of User and call user.save(), or directly call User.find or User.lookup as needed. Notice that these take callbacks for success and error, thats because node js is a totally event driven framework and everything is synchronous. These methods don’t return anything

Lets add a route, create user.js under routes directory.

var User = require('../models/users').get;

exports.authenticate = function(req, res) {
  User.find(req.body.username, req.body.password, function(o) {
    if (o) {
      res.json(o.selectedValues);
    } else {
      res.send(401, "Auth failed");
    }
  }, function(error) {
    console.log(error);
    res.send("Auth failed");
  });
};

And in app.js, add the route.

app.post('/authenticate', user.authenticate);

All done! You now have an app that can connect to the database and authenticate users!

In the next blog, we’ll see how we can quickly assemble a front end