Blog Codealong

LAB: Let's build a blog in Express!

Follow along here: https://github.com/BurlingtonCodeAcademy/express-blog

HTML Endpoints:

• GET / - home page
• GET /articles - list of all articles
• GET /articles/1 - article with id 1
• GET /search - find all matching articles
• GET /publish - form to create a new article
• POST /articles - actually create a new article

JSON Endpoints:

• GET/articles.json - list of all articles in JSON format
• GET/articles/1.json - article with id 1 in JSON format
• GET/search.json?author=alice - list of all articles written by Alice

Data storage

We haven't learned about databases yet, which is fine, because...

The filesystem is a database. 😮

... so for this app, we will store articles as JSON files on disk.

Project Setup

Create a new project named "blog" and run

npm init -y
npm install express

Server Setup

Create a file named app.js with the following code:

const fs = require('fs');
const $path = require('path');
const express = require('express');

const app = express();
const port = process.env.PORT || 5000;
const publicDir = $path.resolve('./public');
const articlesDir = $path.resolve('./articles');

app.use(express.static('public'));
app.listen(port, () => console.log(`Blog app listening on port ${port}!`));

Notes:

• fs and path are NodeJS libraries for dealing with the filesystem. We will use them later.
• we made $path start with a $ so that later we can use a local variable named path without namespace collision

Home page

Our existing server code will handle a default static home page; if we name it index.html then we're good.

Remember -- if you copied and pasted the hello_express server code, you must remove the app.get('/' route, or else Express will say "hello" instead of sending the file.

Create a directory named public and a file named index.html containing:

<h1>Express Blog</h1>

<form method='GET' action='/search'>
  <label>Search by Author: <input type="search" name="author"></label>
  <input type='submit' value='Search'>
</form>

<ul>
  <li>
    <a href="/articles/1">Featured Article</a>
  </li>
  <li>
    <a href="/articles">All Articles</a>
  </li>
  <li>
    <a href="/publish">Publish a New Article</a>
  </li>

</ul>

This page now contains links to all the other pages in the site. Feel free to make it prettier! :-)

Seeding the Database

Create a directory named articles. Inside this directory create a file named 1.json containing something like this:

articles/1.json

{
  "id": 1,
  "title": "How to Cross a Rubicon",
  "author": "Julius Caesar",
  "body": "Lorem ipsum dolor sit amet, consectetur adipiscing elit."
}

Article page is a file plus an API call

Traditionally, a web server generates HTML "on the fly" in response to a web request.

A more modern app will send static HTML/CSS/JS, then that code will run on the client and make a new request for JSON data to fill itself in.

So to make our modern blog app show an article, we need two

1. an HTML file to send on initial page load
2. a JSON route to send the actual article

Viewing a single article (Client-side)

public/article.html

<div class='article'>
  <h2 id='title'></h2>
  <i>by <span id='author'></span></i>
  <p id='body'></p>
</div>
<script>
let articleId = document.location.pathname.split('/').splice(-1);

fetch('/articles/' + articleId + '.json')
  .then((response) => response.json())
  .then(fillArticle)

function fillArticle(article) {
  document.getElementById('title').textContent = article.title;
  document.getElementById('author').textContent = article.author;
  document.getElementById('body').textContent = article.body;
}
</script>

Viewing a single article (Server-side)

Our first route will match /articles/1 and return the HTML for viewing a single article.

Our second route will match /articles/1.json and return the actual article data in JSON format.

Add the following code to the server:

app.js

function articleFilePath(articleId) {
  return $path.join(articlesDir, articleId + ".json");
}

app.get('/articles/:articleId.json', (request, response) => {
  let filePath = articleFilePath(request.params.articleId);
  response.sendFile(filePath);
});

app.get('/articles/:articleId', (request, response) => {
  let filePath = articleFilePath(request.params.articleId);
  if (fs.existsSync(filePath)) {
    let htmlFile = $path.join(publicDir, "article.html");
    response.sendFile(htmlFile);
  }
  else {
    response.status(404).send(`Article ${request.params.articleId} not found`);
  }
});

Now try it out! Visit the "Featured Article" from the home page and see if it works.

Viewing All Articles (Client-side)

public/articles.html

<h2>Articles:</h2>
<div id='articles'>
  <ul>

  </ul>
</div>

<script>
fetch('/articles.json')
  .then((response) => response.json())
  .then(fillArticles)

function fillArticles(articles) {
  let list = document.querySelector('#articles > ul');
  for (let article of articles) {
    let item = document.createElement('li');
    let html = '<a href="/articles/' + article.id + '">' + article.title + '</a>'
    if (article.author) {
      html += ' (by ' + article.author + ')'
    }
    item.innerHTML = html;
    list.appendChild(item);
  }  
}
</script>

Viewing All Articles (Server-side)

In addition to serving static files, the server needs to respond to some routes dynamically.

For example, /articles/1.json will be served statically, but /articles.json will be created on the fly based on the current contents of the public/articles directory.

app.js

app.get('/articles', (request, response) => {
  response.sendFile($path.join(publicDir, 'articles.html'))
})

app.get('/articles.json', (request, response) => {
  let articles = allArticles();
  let data = JSON.stringify(articles);
  response.type('application/json').send(data);
})

function allArticles() {
  return fs.readdirSync(articlesDir)
    .filter(file => file.endsWith('.json'))
    .map(file => JSON.parse(fs.readFileSync($path.join(articlesDir, file))))
    .sort((a,b)=> (a.id - b.id));
}

Notes:

• There's probably a more efficient way to read all the files, using readFile instead of readFileSync, but this works for now.
• Although they look very similar to human eyes, the routes /articles and /articles.json will not overlap with each other, since they are both exact matches. So you can put them in any order.

Publish an Article (Client-side)

public/publish.html

<h1>Publish an Article</h1>

<form method='POST' action='/articles'>
  <label>Author: <input type='text' name='author'></label>
  <br>
  <label>Title:  <input type='text' name='title'></label>
  <br>
  <label for='body'>Body:</label>
  <br>
  <textarea name='body'>
  </textarea>
  <br>
  <input type='submit'>
</form>

Publish an Article (Server-side) (1)

Since the "publish" form will be submitted by the browser (and not by JavaScript), it will send the parameters in URL-encoded format in the request body.

So on the server, we must use express.urlencoded to parse the body and set the parameters inside the request.body object.

app.js

app.get('/publish', (request, response) => {
  let htmlFile = $path.join(publicDir, "publish.html");
  response.sendFile(htmlFile);
})

app.post('/articles', express.urlencoded({extended: false}), (request, response) => {
  createArticle(nextArticleId(), request.body, response)
})

Publish an Article (Server-side) (2)

Before we create an article we must pick a brand new, unused id for it.

app.js

// Pick an unused article id.
function nextArticleId() {
  let articles = allArticles();

  // find the highest id...
  let id = articles[articles.length - 1].id;

  // ...and pick a higher one
  let articleId = id + 1;
  return articleId;
}

Warning: this algorithm has a race condition and will sometimes fail when several clients attempt to create new articles simultaneously!

...but it will be good enough for now. Later we will use a proper database with a good unique id generator.

Publish an Article (Server-side) (3)

app.js

function createArticle(articleId, params, response) {
  let article = {
    id: articleId,
    author: params.author.trim(),
    title: params.title.trim(),
    body: params.body.trim()
  };

  let articleDataFile = $path.join(articlesDir, articleId + ".json");
  fs.writeFile(articleDataFile, JSON.stringify(article), (err) => {
    if (err) {
      response.status(500).send(err);
    } else {
      response.redirect('/articles');
    }
  });
}

Notes:

• it is tempting to pass "params" directly in to the database layer from the route, but it's best to have a separate processing step that lets your application handle security and data integrity issues, including:

  • escaping
  • normalizing
  • validating
  • anonymizing
  • logging

Search

New endpoints:

• /search returns search.html
  • which calls /search.json on page load to perform the actual search
• /search.json returns the results of a search in JSON

The parameters to search are

That's it for now! (We can add other fields later if we want.)

Search (client-side)

search.html

<form method='GET' action='/search'>
  Search by Author: <input type="search" name="author">
</form>

<h2>Search Results:</h2>
<div id='results'>
    <ul>
    </ul>
</div>

<script>
fetch('/search.json' + document.location.search)
  .then((response) => response.json())
  .then(fillArticles);

function fillArticles(articles) {
  let list = document.querySelector('#results > ul');

  if (articles.length === 0) {
    list.innerHTML = 'none';
  }

  else for (let article of articles) {
    let item = document.createElement('li');
    let html = '<a href="/articles/' + article.id + '">' + article.title + '</a>';
    if (article.author) {
      html += ' (by ' + article.author + ')';
    }
    item.innerHTML = html;
    list.appendChild(item);
  }

}
</script>

Notes:

This code depends on document.location.search (the ? portion of the URL) still containing the parameters that were passed from the form when the page was fetched.

Search (server-side)

Since our database is so small, we will load all articles into memory and search through them using a JavaScript iterator (filter).

app.get('/search', (request, response) => {
  response.sendFile($path.join(publicDir, 'search.html'))
})

app.get('/search.json', (request, response) => {
  let results = searchArticles(request.query)
  response.type('application/json');
  response.send(JSON.stringify(results));
});

function searchArticles(params) {
  let results = allArticles().filter((article) => {
    if (params.author) {
      let articleAuthor = article.author || '';
      let targetAuthor = params.author || '';
      return articleAuthor.toLowerCase().includes(targetAuthor.toLowerCase());
    }
  });
  return results;
}

See? Who needs a database? :-)

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