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ExpressJS

ExpressJS

Example of a simple server made using express:

var express = require('express');
var app = express();

app.get('/', function (req, res) {
    res.send('Hello World!');
});

var server = app.listen(3000, function () {

    var host = server.address().address;
    var port = server.address().port;

    console.log('Example app listening at http://%s:%s', host, port);

});

The setup for express application is pretty simple. The amount of coding we needed to do when we used http or net module to create server, set up GET, POST request was huge. But here it’s very simple. All you need to do is invoke express and assign it to a variable (app). It has lots of method pre-build.

Example 2:

Creating the JSON data end point, where I am sending the data back to the client.

app.get('/api/data', function (req, res) {

    res.json({
        'hello' : 'world'
    });
});

If you do a GET on url http://localhost:3000/api/data, then you can see the response (which is a JSON object). Try to do a GET request using POSTMAN to see the Headers.

connection →keep-alive
content-length →17
content-type →application/json; charset=utf-8
date →Thu, 26 Oct 2017 12:01:16 GMT
etag →W/"11-IkjuL6CqqtmReFMfkkvwC0sKj04"
x-powered-by →Express

are the headers for the GET request. The content-type is application/json already (we didn’t set this in the code).

So you can see in less then a minute we can build api server ground up with a couple of commands.

Example 3:

Making an api server which fetches data form the mongodb cloud server and gives it as response to the client.

var express = require('express');

var mongojs = require('mongojs');
var db = mongojs('mongodb://adminamit:amit123@ds121955.mlab.com:21955/amitmongodb', ['users']);// connecting to cloud db to get the list of users


var app = express();

app.get('/', function (req, res) {
    res.send('You are at /');
});

app.get('/api/v1/users', function (req, res) {

    // here we are going to go to mongodb and whenever a user hits on /api/v1/users I am going to query the could interface and find all the records
    db.users.find({}, function (err, docs) {
        if (err)
        {
            res.status(500);
            res.send({
                err: new Error(err)
            });
        }
        else
        {
            res.json (docs);
        }
    });
});

var server = app.listen(2000, function () {

    var host = server.address().address;
    var port = server.address().port;

    console.log('Example app listening at http://%s:%s', host, port);
});

This is typically an end to end api interface which is just build using express mongodb and nodejs.

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People generally don’t want to put their routes inside their main file (index.js). So for that purpose we create a new file generally named as routs.js. In this file we define all the routes to the application.

See this file. It is the main file index4.js and it is calling function written in routes.js file. The routes.js file looks like this:

var mongojs = require('mongojs');
var db = mongojs('mongodb://adminamit:amit123@ds121955.mlab.com:21955/amitmongodb', ['users']);// connecting to cloud db to get the list of users

module.exports = function (app) {// this function takes app as its argument

    app.get('/', function (req, res) {
        res.send('You are at /');
    });

    app.get('/api/v1/users', function (req, res) {

        // here we are going to go to mongodb and whenever a user hits on /api/v1/users I am going to query the could interface and find all the records
        db.users.find({}, function (err, docs) {
            if (err)
            {
                res.status(500);
                res.send({
                    err: new Error(err)
                });
            }
            else
            {
                res.json (docs);
            }
        });
    });

    return app;
};

Next you can separate your db configuration using another file (./dbconfig.js). So we are trying t modularize our code into peace.

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