jwatkins0101 / lesson-week_10-day_01-express

Express API

Objectives

By the end of this, developers should be able to:

• Write five CRUD endpoints for an API resource using Express and Javascript.

Preparation

1. Create a new branch, training, for your work.
2. Checkout to the training branch.
3. Install dependencies with npm install.

Overview

According to its maintainers:

Express is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

Express, like Rails, can be used as an API. In fact, building APIs in Express, led to the rising popularity of Node.

Express can be used for full-stack applications (those that have server-rendered views). However, we will use it purely as an API.

Install Express

• https://expressjs.com/en/starter/installing.html

Demo: "Hello World" API

• https://expressjs.com/en/starter/hello-world.html

Let's take a look at a super simple Express application. Open up examples/tiny_server.js. This is a fully functional Express API, in just four lines of code! We can run it like this:

node examples/tiny_server.js

And we can make a request to it by visiting localhost:4741

Code-along: Library API

• https://expressjs.com/en/starter/basic-routing.html

Most apps need to do a bit more than always sending back "Hello world". To get some more exposure to Express, let's build out a minimal API in examples/medium_size_server.js that that we can use to keep store books for a library. Because we haven't learned how to integrate a database into Express yet, we'll just store our data in memory.

Our app will have three routes available:

• GET /books: respond with JSON of all books, like index in Rails.
• GET /books/:id: respond with JSON of one book, like show in Rails.
• DELETE /books/:id: delete book based on id, then respond with success. We can not use the browser URL to test our delete requests so let's use an application Postman to do so.

Our API we'll need more functionality than the previous example. Still, we'll recognize a lot of the same patterns. What were those req and res parameters exactly?

req req stands for request, and it contains lots of info about the incoming HTTP request that the server receives. It contains things like the URI path, HTTP headers, the HTTP verb (GET, POST, etc.), query parameters, parameters from dynamic route segments, and more.

res res stands for response. We use this object to put together a response, and then we send that response with methods attached to this object. res.json signals to Express that we're done working on our response. It's analogous to Rails' render method. If you don't use a terminal handler, Express will keep the connection open waiting for one. You and Express will both be frustrated and confused. Here's a list of terminal handlers. You will use res.json and res.sendStatus most frequently. Some of these are:

Response method	What it means
res.json(jsObject)	Send a JSON response.
res.redirect()	Redirect a request.
res.sendStatus()	Set the response status code and send its string representation as the response body.

To get a little more specific, the req object is a http.IncomingMessage object. The res object is http.ServerResponse object. Notice that the above links point to the NodeJS docs. These objects are actually native to Node, not Express, Express uses them everywhere.

Additional Resources

• Express - Node.js web application framework
• Understanding Express.js
• How body parser works

License

1. All content is licensed under a CC­BY­NC­SA 4.0 license.
2. All software code is licensed under GNU GPLv3. For commercial use or alternative licensing, please contact [e-mail].