ExpressJS Workshop for DecodeMTL Full-Stack Bootcamp

Your express way to the web development world!

Basic instructions

⚠️ ⚠️ Do this workshop in the same Cloud9 workspace as your Reddit API.
Different exercises will require different NPM packages. This will require you to use npm install --save to get these packages.
An index.js file is made available to you. It contains the code to load the Express library and make a server that listens to the correct port for Cloud 9. You can copy the code as an easy way to get started.

Exercise 1: Getting started!

Add an endpoint /hello to your web server. Make it return the HTML string <h1>Hello World!</h1>.

Exercise 2: A wild query has appeared!

Improve your /hello endpoint so that if it's called as /hello?name=John, the response will be <h1>Hello John</h1>. If no name query string parameter is provided, keep doing the same thing as exercise 1.

Exercise 3: Operations

Add an endpoint /calculator/:operation to your web server. The valid values for :operation are add and multiply. This endpoint will also accept query string parameters num1 and num2. If they are not passed, they should be set to 0. This endpoint should return a JSON string like this:

{
  "operation": "add",
  "firstOperand": 31,
  "secondOperand": 11,
  "solution": 42
}

NOTE: query string parameters -- the part after the ? in a URL -- are different conceptually from the request parameters, which are part of the path. For example here you are asked to use :operation as request parameter. In express, you do this by making your app.get('/calculator/:operation', ...). The : before operation will tell Express that this is a request parameter. You can access it using the request.params object instead of request.query which would be for the query string. In general, while the query string is reserved for either optional values or values that can vary wildly, we will use request parameters when they can themselves represent a resource. Here, we are looking for the calculator resource, and under it for the add "sub-resource". Of course this is our own terminology and in general it's up to us to decide what our URL schema represents.

If :operation is anything other than add or multiply, you should use res.status to send an appropriate error code. In this case, the most general possible code is 400 Bad Request.

Exercise 4: Retrieving data from our database

The goal of this exercise is to create an endpoint /posts that retrieves the contents of the posts table of your reddit database using the getAllPosts function you created in the previous workshop, and display them to the user using an HTML <ul> list.

As a first step, you'll have to load up the RedditAPI constructor and create a new instance. To do this you'll also need to setup a database connection in your web server file so you can pass it to the RedditAPI constructor.

Using your getAllPosts function from RedditAPI, retrieve the latest posts. Then, you should build a string of HTML that you will send with the request.send function.

Your HTML should look like the following:

<div id="posts">
  <h1>List of posts</h1>
  <ul class="posts-list">
    <li class="post-item">
      <h2 class="post-item__title">
        <a href="http://the.post.url.value/">The title of the post</a>
      </h2>
      <p>Created by Username</p>
    </li>
    <!-- ... one <li> per post that getAllPosts returned -->
  </ul>
</div>

To build this string of HTML manually is quite cumbersome, and we will see a better way to do it later.

Exercise 5: Creating a "new post" HTML form

In this exercise, we're going to create an endpoint /new-post that will simply send an HTML <form>. Here's the code for the HTML form:

<form action="/createPost" method="POST"><!-- why does it say method="POST" ?? -->
  <p>
    <input type="text" name="url" placeholder="Enter a URL to content">
  </p>
  <p>
    <input type="text" name="title" placeholder="Enter the title of your content">
  </p>
  <button type="submit">Create!</button>
</form>

⚠️ This exercise is EASY. Don't look too much into it. It's only a preparation for the next exercise. It's almost as easy as exercise 1. All you have to do is send an HTML string as a response.

Exercise 6: Receiving data from our form

In this exercise, we will write our first POST endpoint, /createPost.

In the code of app.post('/createPost'), we will be receiving the form data from step 5. This data will be sent by the browser when the user presses the submit button. The form will instruct the browser to make a POST request (because of the method), and the resource will be /createPost because of the action parameter.

The way a browser submits a form is by taking all the <input>s in the form, finding their values, and building a query string automatically. If the method is set to GET, the query string will be added to the end of the action URL with a ?. If the method is POST, the query string will be sent as the request body. The request body is not apparent directly in the browser window, but you can see it if you open your Dev Tools.

In a previous exercise, you were able to retrieve data from the query string by accessing the request.query object. This object is automatically created by Express if there is a query string in the URL. Request bodies do not get parsed automatically by Express. The easiest way to parse the request body is to use an ExpressJS middleware. Start by reading up about middleware and what they do. We will talk about them more in detail in further lectures.

The bodyParser middleware can parse the request body that is sent by a browser. Before reading the form data, you will have to install the body-parser middleware with NPM, require it in your server code, then load it with app.use.

Form data is sent by default using the urlencoded format. The documentation explains how to make bodyParser read urlencoded request body. After adding this middleware, the form data will be available as request.body. It will be an object that contains the data submitted by the browser.

Once you are familiar with the contents of request.body, use the createPost function from RedditAPI to create a new post that has the URL and Title passed to you in the HTTP request. Since you don't have a user system yet, set the userId to 1 when you call createPost.

Once the data is inserted successfully, use response.redirect to send the user back to the /posts page you setup in a previous exercise.

Exercise 7: Using a template engine

Tomorrow, we will learn about ExpressJS template engines in class. Template engines are useful if we want to send HTML.

The simplest way to send HTML to the browser is to use response.send, and pass it a string of HTML. This is what you had to do for exercises 4 and 5, and it has a few disadvantages:

The HTML is mixed up with the web server code, which is less than ideal. It makes it harder to see the logic of the web server.
Generating dynamic HTML can be tedious and error-prone: you have to do string concatenation, close your tags properly, and be sure to escape your HTML to avoid injection attacks.
Every time you want to change the HTML code, you have to restart your web server. While this may not be a huge issue, it can be avoided if the HTML is in a separate file.

There exist tons of different template engines that work with Express. The idea behind a template engine is super simple: it's a function that takes some data -- usually an object --, and returns HTML based on the so-called template. The difference between the various template engines that exist is the syntax they use for expressing the transformation of data to HTML.

Once you know one or two template languages, learning new ones is quite easy. For this course, we're going to use the Pug template engine, which was previously known as Jade.

The goal of this exercise is to practice writing Pug templates, to get us ready for our big Reddit Clone project. To do this, we're going to use Pug to refactor exercises 4 and 5.

Here are the steps to follow:

From your terminal, install the pug NPM package.
From your index.js file, set Express to use the Pug engine by adding the following line:

app.set('view engine', 'pug');

In your project root, create a directory called views. This is where Express will look for your templates.
Create a new file called create-content.pug in the views directory.
Paste the following content in the file:

form(action="/createContent", method="POST")
  p
    input(type="text", name="url", placeholder="Enter a URL to content")
  p
    input(type="text", name="title", placeholder="Enter the title of your content")
  button(type="submit") Create!

Notice how the Pug code is much shorter than its HTML counterpart? This is because Pug uses indentation rather than opening and closing tags. This template actually has no dynamic parts to it, but it's still nicer to write it than the HTML document, and it's separated from the web server code!
In your app.get('/createContent') code, remove all the HTML you created, as well as the res.send. Replace them with the following single line of code:

res.render('create-content');

Restart your web server and verify that you are getting the same HTML.
Let's do the same thing for Exercise 4. This time, we have some dynamic data. We will need to loop through the array of posts and display it using a Pug template. 1. Read the documentation on iteration with Pug. We're interested in the each loop here. Make sure you understand how it works. 2. In your web server code, inside the app.get('/posts') code, replace the manual rendering with a call like this:
```
res.render('post-list', {posts: posts});
```

3. In your views directory, create a file called `post-list.pug` and try to recreate the same output as you did with HTML. You will have access to a variable called `posts`, that will have been transmitted by the call to `render`. You will need to use the `each` functionality of Pug to do this.

Exercise 8: Layouts

This exrcise expands on the previous one. In the previous exercise, we saw how to generate dynamic HTML by using a template engine. This is great, but normally we have to send a full HTML page rather than a part of a page.

Pug lets us do this using inheritance. We start by defining a "layout", which is simply a template with some placeholders. Then, when we render our main template -- the one you created in the previous exercise -- we specify how the placeholders should be filled in.

For this exercise, we're going to create a basic layout. In your views directory, create a file called layout.pug with the following content:

doctype html
html
  head
    meta(charset="utf-8")
    block title
      title The Default Title
  body
    block content

Then, modify your post-list.pug from the previous step to use this layout. To do this, you'll have to add one extends line at the top of your file, and move the rest of the template inside a block. If you are unsure how to do this, make sure to read the documentation about extends and inheritance.

Hint: This should not be more complicated than adding a line or two, and indenting some code!

CHALLENGE: Let's add a bit of CSS!

Now that you have a layout for your "site", you should easily be able to include a CSS file :)

In the head section of your layout, add the following line:

link(rel="stylesheet", href="/files/styles.css")

That was the easy part. If you have done this correctly, when you refresh the /posts page your browser will try to load a file /files/styles.css from your web server. This will result in a 404 error, because your server doesn't know how to respond to this request -- yet!

In your project, create a directory called static_files, and inside create an empty file called styles.css.

Now we have to figure out how to make your web server serve this file. Tomorrow, we will learn about ExpressJS middleware, functions that can respond to requests without any intervention from your part. One such middleware is the static middleware. You can point it to a directory on your computer, and it will automatically "res.send" any file that is requested from this directory.

For this challenge, you have to figure out by yourself how to add the static middleware to your web server. Your middleware should only be active if the URL starts with /files, and it should look in the static_files directory for any file that matches. This way, when your browser requests the URL /files/styles.css, your middleware should be able to send the file called styles.css under the static_files directory. Note that the name of the directory and the path prefix in the URL are not related to each other.

You are too good for this!

Well, it seems like the day has not ended and you finished everything. Watch this course from Google on Client-Server communication on Udacity to advance your understanding of HTTP!

plllmg/expressjs-workshop