So our Express app object, which is our server, is listening for requests, but how will it know which requests to respond to and what to do when it does?

To do this Express keeps a list of items called ‘routes’.

Each route has three components:

1. A HTTP request method
2. A URL path (AKA endpoint)
3. A handler function

When the server receives a request, it looks at the request’s URL path and request method. If it has a route that matches both, then it responds to the request by running the handler function associated with the matching route.

This process of matching a request to the right handler function is called “routing”.

We add routes to our server to tell it which requests to respond to, and what to do for the response in each case.

Adding a Route

To add a route using Express, you call the function for the request method, using the URL and your handler function as parameters.

Let’s try adding a GET route.

Update server.js like so:

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

app.get('/hello', function (request, response) {
  response.send('Hello World!');
});

app.listen(8080, function () {
  console.log('Server has started listening on port 8080.');
});

Our new lines use the get function, which adds a route for GET requests. GET requests that are sent to the /hello endpoint trigger our handler function, which sends back a simple text response of ‘Hello World!’.

Make sure your changes to server.js are saved.

Now in your terminal press ctrl + c to stop your server running and run your server again with node server.js.

You will see the “Server is listening” message again.

So now that it’s running, how do we send a GET request to it? By using our trusty web browser of course.

Open a new browser window or tab and type in the address below:

• For Cloud9 Environment

  https://WORKSPACE-USERNAME.c9users.io:8080/hello

  Don’t forget to replace USERNAME with your Cloud9 username and WORKSPACE with the name of your workspace.

• For Local Environment

  http://localhost:8080/hello

Then press ENTER and you should see the “Hello World!” message displayed in your browser like a webpage.

It will look a little like this:

Every time you request a webpage in your browser, it is doing a GET request. Sending GET requests is probably the most common daily activity in the world today.

Looking more closely at handler functions

The second parameter we supplied for the route was a handler function.

A handler function is just a regular Javascript function which app will invoke when a request matches the associated route. app passes two parameters to it as well: one that contains the request data, and one to use to send a response.

Let’s look at the handler function from the /hello route above:

function (request, response) {
  response.send('Hello World!');
}

request contains all the information about the request that matched this route. We don’t use it in this example. There is a massive amount of information in request and we will talk about this more in step #7.

response is what we use to send a response back to the client. It has several different functions that we can use to do this. In this example we used response.send().

Exactly what steps you perform in each handler will depend on your application and the specific route that it belongs to.

Try it yourself

Now you know a little more about routes and handler functions, try adding this new route yourself.

Here’s what you need to know:

• request method is get
• the endpoint is /chocolate
• the response should be Mmmm, chocolate ...

Test it by going to in your browser:

• For Cloud9: https://WORKSPACE-USERNAME.c9users.io:8080/chocolate
• For local: http://localhost:8080/chocolate

Check the solution below if you get stuck.

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

app.get('/chocolate', function (request, response) {
  response.send('Mmmm, chocolate ...');
});

app.listen(8080, function () {
  console.log('Server has started listening on port 8080.');
});