This tutorial will walk you through creating a very simple Express.js backend, how to run it and how to add some routes.

It assumes that you already have nodejs installed. If not, follow that link and download the latest version.

The goal of this tutorial series is to create a backend for a venue app, where we can store venue locations and menus and customise a 'favourite venues' list for each user.

Setting up

Once we have installed Node, we should have a command line instruction called npm. Open up a new Terminal window and navigate to a desired project directory. Run npm init. A field package name should pop up, feel free to name your project anything, but we will use 'venuewatcher'. Keep hitting enter to leave the rest of the fields as their default value. Note: If running npm init did nothing, you have not correctly installed Node.

Now we have a file called package.json which contains metadata about our project. This file can contain things like author, description, name, version and scripts.

You might have noticed the "main" field was set to index.js. This is our entry point for the application, meaning execution of our program will start from here. Kind of like a main function in C.

Go ahead and create a new file called index.js. Leave it blank for now.

Scripts are a useful shortcut to have in your package.json and we are going to add one now. Open up package.json and in the "scripts" section, under "test", add the line:

"start": "node index.js"

This will allow us to start our server using the command npm run start. This comes in handy if our startup commands become more complex.

We are now ready to start on our server.

Starting our server

Firstly we want to install the express.js package. Do this by navigating to our project directory and typing npm install express.

Then in our index.js, we want to import that express package to be something we can use by adding the line:

const express = require('express')

This require statement has imported the express function from the express package.

Now we can initialise an express app by calling this express function by adding the line:

const app = express()

Finally, we can start our express app by using the listen method. The following lines achieve this:

app.listen(5000, () => {
  console.log('Server started!')
  console.log('Listening on port 5000')
})

Let's break this down a little bit. First we are referencing our app and calling the listen method on it. This just means that we will listen out for any events that occur on the specified port. In this case, we are using port 5000, hence we have passed 5000 as the first argument to listen.

The second argument to listen is a function that we execute as soon as the app is started. It is good to get some feedback from your server that things are working properly, so indicating that the server has been started and which port it is listening on is helpful.

Now go back to our command line, execute npm run start, and we should see our nice helpful messages telling us that the server has been started and it's running on port 5000.

Adding routes

Routing

Routes are extensions to our base url which let us categorise different sections of our backend server.

Express makes it extremely easy for us to add routes to our application.

After our line where we create the app express object, we want to add the line:

var router = express.Router()

This will initialise a new Router object which we can add our routes to. We also need to connect this new router to our express app, and we do that using middleware.

After we have created our router, we can connect it to our app and specify that all data transfered to and from our backend will be in JSON format using the following lines:

app.use('/', router)
app.use(express.json())

Easy! Now we just need to add routes to our router!

GET

There are four request types GET, POST, UPDATE, DELETE. We will firstly look at the most simple two, GET and POST.

The GET request is pretty self explanatory and refers to collecting data from a backend. We can add a get route to our router by adding the following line, ensure you add this after you initialise the router object and before the app.listen.

router.get('/venues', (req, res) => {})

To this get function, we have passed the route ("/venues") as the first parameter, and a callback function as the second. Right now, our callback just takes in the arguments req and res and does nothing. req refers to the request payload, and res the response payload.

So now if we were to run our application and send a request to localhost:5000/venues?name=johnscafe we would trigger this route with the query parameter name set to "johnscafe" and the callback would be called.

Before we try running it, we want to get some kind of response from our server if we send it a request. Let's add a kind of "database" into our application. Under the router object you created earlier, add the line:

let database = { johnscafe: 'Rated 10/10!' }

Now in our GET callback function body add the following line:

res.send(database[req.query.name] || 'Venue not found!')

This checks if name is in our database, if so return the corresponding value. Otherwise return "Venue not found!". req.query stores any query parameters we pass in after the ?. If we wanted to send multiple, they get separated by an &.

res.send simply sends our reply from this route.

Good, now we have set up our server and created a GET route and let it send a response. Now we need to test it.

Sending requests

Start by spinning up your server using npm start and make sure there are no errors.

There are many testing platforms for sending requests to routes, the one that I use is Advanced Rest Client (ARC) by MuleSoft.

Assuming you are using ARC, once you open it your window should look something like this:

Set the request type to GET, set the Request URL to http://localhost:5000/venues?name=johnscafe and hit enter. You should see a review "Rated 10/10!" come up as the response.

Try changing the name of the venue we are requesting and see what the server responds with.

POST

The second route type we want to tackle is the POST route. This is concerned mainly with sending data to the backend.

Our POST request should manipulate the database in some way. Add a new post request using:

app.post('/venues', (req, res) => {})

The data sent to a POST request is accessed using req.body.[field]. Our users will pass in a review for a restaurant in JSON format, where the key will be the name of the restaurant and the value the rating.

We can write all of these reviews to our databse using Object.assign. In our POST callback body, add the line Object.assign(database, req.body). This copies everything from our req.body to our database. After this, send a string in response confirming that the operation was successful.

Now let's try testing our POST request. Open up ARC again, set the request type to POST and set the request URL to http://localhost:5000/venues. You will have noticed an extra tab show up called BODY below where you input the post request payload. Set the type to JSON and in the body section input something like {"crumbs": "Rated 9/10"}. Send the request and make sure your success message is returned.

Now, try making a GET request to http://localhost:5000/venues?name=crumbs and we should see our newly added venue review!.

In our next article we will look at integrating MongoDB.