Hello Express

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Hello, Express!

In this lesson you will create a trivial web application in Express and deploy it to Heroku, where it will be visible to everyone on the Internet.

Hello, File!

In your Terminal, make a directory called hello-express with mkdir hello-express
Immediately enter the directory with cd hello-express
run npm init -y to create a fresh package.json file
run npm install express to load the express package into this project
Launch the Visual Studio Code text editor and open this hello-express directory
Inside this directory make a file named server.js and fill it with the following code:

const express = require('express')
const app = express()
const port = process.env.PORT || 5000

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

app.listen(port, () => console.log(`Listening on port ${port}!`))

Hello, Localhost!

Go back to the Terminal and run the app with node server.js
Visit http://localhost:5000/ to see it running on your own computer.

Hello, Package!

A package file contains information about how to build and run your app.

In Code, open the file named package.json and add the start script line like this:

{
  "name": "hello-express",
  "scripts": {
    "start": "node server.js"
  }
}

Note that the code after start is exactly what you typed in the shell to run the app locally.

You can test this locally by running npm start and refreshing your browser.

Hello, Git!

Now make a git repo for your app.

Remember to press CTRL-C to stop the server

Make sure you are in the correct directory with pwd

pwd           # the response should end with "hello-node"
git init
git add .
git commit -m "first commit"

Hello, Heroku!

Heroku uses git for its deploys. Whenever you push a new version of your git repo to Heroku, it automatically deploys the app to the cloud.

heroku create
git push heroku master

If all goes well, you will see a URL on your console, something like this:

remote: https://damp-retreat-99529.herokuapp.com/ deployed to Heroku

Visit this URL in a web browser using copy-and-paste, or use this handy shortcut from the console:

heroku open

High Five!

If you are working with a partner, give them a high five.

If you are alone, give yourself a high five.

high five

You deserve it!

image by Pandark (CC-BY-SA)

Hello, You!

Now go back to Code, and modify the app so instead of saying "Hello, World!" it says something clever and personalized.

Once you've made the change...

test it locally
add the changed file to git and commit the change
re-deploy to Heroku
reload the web page and read your new message
give yourself a high five!

Parameters in Express

The special character : means "this is a path parameter"

Example:


Path:	`/hello/Gandalf`
Route:	`/hello/:friend`
Params:	`{friend: 'Gandalf'}`

Express will grab the value from the path itself, and put it into the request.params object for you to use later.

Hello, Query Friend!

Now change your "Hello, Express" server to also have the following route:

app.get('/hello/:friend', (request, response)=> {
    response.send('Hello, ' + request.params.friend + '!');
});

Prove that it works by visiting http://localhost:5000/hello/Gandalf (or use your own name)

Resources

Some other Node/Express tutorials: