Express is a web application framework for building the business logic of web sites using the Javascript programming language. It was also developed using Javascript and runs on the Node.js platform as an installable package. The first release, version 0.12, was on 22 May 2010 and it continues to be upgraded due to large developer support in the Javascript open source community.
The express.js main repository is found at https://github.com/expressjs/express, and it is maintained under the MIT license so you are free to make a copy of it. The website is expressjs.com. Express is used by companies like Fox Sports, PayPal, Uber, and IBM to run their backend systems. Express is used for:
- Creating routes.
- Implementing Representational State Transfer (REST).
- Improving application performance.
- Inserting HTTP helpers (redirection, caching etc.).
In this article, I will be building a web application with an express server which will access different endpoints. To get started, you will need to have the following tools installed:
I like to think of the relationship between a client and a server as a waiter/waitress in a restaurant. When you select something on the menu, the waiter will return with your choice as represented by the diagram below:
An Image Representation of the Client/Server Model:
The first thing I'll do is create a folder on my computer and name it 'Working With the Express Framework.' I have also added the repository to GitHub so you can access it via this link by making a clone of the repository.
Open the folder in VS Code or your preferred editor, and access your terminal. Type into the terminal; npm init -y. If you've cloned my repository, you should use the npm install command which installs the node_modules on your local device. This initializes the node package manager which gives us access to all the modules within Node.js, including express. Next, I'll type npm install express --save. This line tells our package manager to include express in our project so that we may utilize it in our application. Make sure to follow the prompt that comes up in your terminal to enter information about the application. These steps are not necessary if you are using the files I have provided.
You will notice that a new file has been automatically created inside our previously created folder and it is called package.json. This folder contains important configuration information for our application to run successfully. If you are familiar with JSON you will understand how data is stored in a .json file but if you are new to the Javascript ecosystem then I suggest you learn about the JSON syntax by watching this youtube video from freeCodeCamp or read this article: JSON Tutorial: Learn JSON in 10 Minutes.
Your package.json file looks similar to this:
{
"name": "working-with-the-express-framework",
"version": "1.0.0",
"description": "application description",
"main": "server.js",
"scripts": {
"start": "node server.js"
}
}
The "name": represents the field, and "working-with-the-express-framework" represents the value of the field. Some of the information in this file was captured from the responses when you created the application using the terminal. If this was represented in tabular form, it would look something like this:
| name | version | description | main |
|---|---|---|---|
| blog | 1.0.0 | working-with-the-express-framework | server.js |
Now, in order to use express we will need a folder to write code in. Create a file and name it server.js, this will be the folder we use to configure our server.
Configuring The Server
You will need to write the following in server.js:
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.sendFile(`${__dirname}/index.html`, (err) => {
if (err) {
console.log(err);
res.end(err.message);
}
});
});
app.listen(2000, () => {
console.log('Server has started listening on port 2000');
})
The line that says const express = require('express') imports the express library into our file. We then define the variable app, which initializes the app. The app.get('/') method is used to read the requested path and send the response which is an index.html file. We then tell our server to listen on port 2000.
Let's go ahead and create our index.html which is the home page of our web site. Create it in your folder, please note that the name of your file should have the .html extension and should be the same as the file name in server.js. Writing some HTML file will be displayed in the browser. If you can't come up with anything, refer to this project I made for inspiration. Or you could write the following code in your html file:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<link id="main-css" rel="stylesheet" href="styles.css">
<title>Types of Dinosaurs</title>
</head>
<body>
<div>
<h1>Types of Dinosaurs</h1>
</div>
</body>
</html>
For a better understanding of the HTML language, you can have a look at my blog post, Exploring the Hypertext Markup Language which goes into details. The text we have written in our HTML file will render as a web page on the port 2000.
Styling The Web Page
Add the following code to your server.js file; app.use(express.static('public'));. This ensures that all items inside the "public" folder are included with our HTML file. Now you can create a folder called public in the root of your folder, then create a file inside it and name it styles.css. Add some styles to the file to improve the HTML file like this:
*{
background: red;
}
h1{
text-align: center;
}
Spinning Up the Server
Type npm run start into your terminal. After a few seconds you should notice the terminal output that says "Server has started listening on port 2000." This indicates that your application is live and you can visit it on your browser. If you open your browser and search for localhost:2000, your web page will be loaded to the screen.
Installing Nodemon
You will notice that every time you make a change to your source files and save, you will have to manually restart your server. This can be a tiresome task, so Node has a package to assist with this and to install it, type into your terminal; npm install nodemon. If it was installed successfully, you will see "nodemon" under the "dependencies" field in your package.json file. This time, if you make changes to your source files, you won't have to manually restart your server.
NB: Npm commands will not work without an internet connection.
The dependencies field inside package.json will now look like this:
The Waiter and The Client
This is a simple example of a server that accesses a web page when requested by the user. This relates to the scenario I previously mentioned of a waiter in a restaurant. When a user asks for the available web page, then the server/waiter returns a relevant response. The advanced web applications we use everyday are an improvement from this concept, they just scale when you consider factors such as user base, security, and database management.
If you enjoyed this article, let me know your opinion.