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 yarn 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.

yarn add express
touch index.js

Note:

We've been running yarn global add <package name>to install the package globally. You'll want to reserve global add 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 (req) and response to send back to the client (res). Calling the .send function on the response sends a string back to the client.

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

app.get('/', function(req, res) {
  res.send('hello brian')
});

app.listen(3000)

More Route Styles

By putting a colon before a string in our route, we can create routes with different variables, or parameters. These parameters are automatically pulled out for us by Express and can be accessed via the req.params object.

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

app.get('/', function(req, res) {
  res.send('hello brian')
});

app.get("/greet/:name/:lastname", function(req, res) {
  res.send("Hello " + req.params.name + " " + req.params.lastname)
});

app.get("/multiply/:x/:y", function(req, res) {
  res.send("The answer is: " + (req.params.x * req.params.y))
});

app.get("/add/:x/:y", function(req, res) {
  res.send("The answer is: " + (parseInt(req.params.x) + parseInt(req.params.y)))
});

In addition to having routes where different portions of the URL are different paramaters, we can use the generic string of the URL in our route logic using the wildcard.

app.get("/add/*", function(req, res) {
  let myParams = req.params[0].split("/")
  const result = myParams.reduce(function(total, num) {
    return total + parseInt(num)
  }, 0);
  res.send("The answer is  " + result)
})

This will give you a URL like http://localhost:3000/add/5/3/3/2/3 and give you an answer.

Running your Project

If "main": "index.js" is in your package.json, then running nodemon will automatically start your project and serving your file.

Intro to Express