First Express App with Routes

To create a web application using Node, we're going to import a web app server framework called Express. We can install this as a package using npm, then use it to create applications.

Setting up a project

Create a new folder for use with the project using mkdir node_calculator, and cd into cd node_calculator

First we want to start a new project by going npm init. Follow the instructions, clicking enter through the statements. you many want to specify a version number, but most default options should be fine. It will also specify an initial file to use. The default is index.js, and this acts as the "entry point" into our app.

Basic Express Setup

Before we do anything else, let's set up a basic Express app. We need to install our dependencies, create the index.js server file, and create an index for our homepage.

npm install express
touch index.js

Note:

We've been running npm install -g <package name>to install the package globally. You'll want to reserve -g for packages that will be run in the command line.

index.js

The following example shows how to get routes working in Node. A route is a combination of a URL pattern + HTTP Verb (get, post, put, delete). These verbs represent a method for the request.

Each route is called on our Express app, and takes a URL pattern and a callback function. The callback function gives us back the request (request) and response to send back to the client (response). Calling the .send function on the response sends a string back to the client.

const express = require('express');
const app = express();

app.get('*', (request, response) => {
  response.send('hello brian');
});

app.listen(3000);

Conditional Response

const express = require('express');
const app = express();

app.get('*', (request, response) => {
  response.send('hello brian');
});

app.listen(3000);

Get user input from the request path:

request.path

Respond based on what path is requested.

if( request.path == '/foo' ){
  response.send('yay');
}else{
  response.send('boo');
}

Pairing Exercises:

Curl

Use curl to make a request to express from the terminal.

Request and Response Objects

See what else is in the request parameter by console.loging it.

See what else is in the response parameter by console.loging it.

Local Network

Find your IP address. Put the address into your browser and request your server through the local network. Ex. 168.4.3.1:3000/foo

Change the address of your server with your pair.

Put your server address into the class slack channel.

Express Server on the Internet

Create an express server and put it on the internet using ngrok:

Run express:

node index.js

Open a new terminal window and start ngrok (what directory you are in doesn't matter)

cd my-ngrok-download-directory
./ngrok http 3000

Put your ngrok server address into the class slack channel.

HTML Response

Put HTML in response.send:

Paste this above the app.get('*'

app.get('/papaya', (request, response) => {
  response.send('<html><body><h1>Hello</h1><a href="#">wow</a></body></html>');
});

What happens when you visit it using curl? curl localhost:3000/papaya

What happens when you visit it in the browser?

Ports

Create another directory and express server.

Listen on a different port.

Request from both servers.

Try to listen on the same port.

Paths

If the user requests bananas in the path, send back bananas.

If the user requests apples in the path, send back strawberries.

Further

If the user requests /charizard, send back information about charizard. If the user requests /pikachu, send back information about pikachu. If the user requests /squirtle, send back information about squirtle.

Intro to Express