First Express App with Routes

Managing Packages

The manager we use to keep track of these different groups of modules is called npm, short for Node Package Manager. Think of a node package as an external library, like jQuery, but on the back-end. We can run npm to install different packages, which are stored in a file called package.json. We'll get into installing packages when using Express.

Express

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.

Our first Express App

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.

npm install --save express
touch index.js

Installing nodemon

npm install -g nodemon

If we just ran node nameOfFile.js, node will not update if we make changes to the file. Nodemon solves this problem by updating the file once changes have been made. Install nodemon (only have to do this once), we will run our apps using the syntax

nodemon nameOfFile.js

Note: We've been using the --save and -g flags when installing using npm. --save is used when you want to add the package to your package.json file. -g installs 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 (req) and response to send back to the client (res). Calling the .send function on the response sends a string back to the client.

var express = require('express');
var 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.

var express = require('express');
var 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) {
  var myParams = req.params[0].split("/")
  var 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.

Routes