Express Cheatsheet

express-how.md

Intro to the Backend

Web works via browsers and servers.

• Users type in urls, click on links, submit forms
• The browsers sends a request
• a server receives the request and responds
• may response with html, files, json, etc.

Servers can be written in javascript with a javascript run time, and there are three of them:

• node
• deno
• bun

node is the most popular cause it's been around the longest.

Backend frameworks

Framework: A system of libraries, practices and conventions that'll make building a particular type of application easier.

Write servers in node from scratch can be tricky and there are several frameworks created in the node ecosystem.

minimalist (basic routing functionality)

• express (most popular)
• koa
• fastify

battery included frameworks

• NestJS
• FoalTS
• Sails

Setting up an express project

• open a terminal to an empty folder

• confirm you have node node --version

• create some files touch server.js .gitignore .env

• list the things we want git ignored

.env
/node_modules

• create a new node project (package.json) create it by running npm init -y npm: node package manager init: to initiatlize a new package.json -y: accept all default values

• If not already installed, install nodemon globally (npm install -g nodemon)

  • nodemon is a tool that will turn on file watchers when you run a program, if you update a file, it'll restart

• update the scripts in your package.json

  "scripts": {
    "start": "node server.js",
    "dev": "nodemon server.js",
    "dev2": "node --watch server.js"
  },

Note: the --watch flag is for new versions of node

Writing basic express server

//*************************** */
// DEPENDENCIES
// Brings things from libraries and other files
//*************************** */
// require('thing'): it will return the exported value of the library or file we specify

//import the express library
const express = require("express")


//*************************** */
// Create Express Application Object
// This is the center of our express universe
//**************************** */
// express(): returns an express application object

const app = express()


//**************************** */
// MIDDLEWARE
// Special Utilities that run before our routes
//****************************+ */


//*****************************
// ROUTES
// Which function should run for differnt (method/url) pairs
// ****************************
// methods: GET, POST, PUT, DELETE
// url: anything after the domain so xyz.com/cheese -> url: /cheese

// a GET request to the ROOT url or "/" xyz.com/ => "/"
// app.get(url, function)
// function: (request, response) => {}
// req (request): an object with details about the request
// res (response): an object with functions to send the response
app.get("/", (req, res) => {
    // res.send(something) will send the response based on the input
    // an html string: will send back as html
    // js array or object: will send back json
    // string: sends back as text
    res.send("<h1>Hello World</h1>")
})



// *****************************
// TURNING ON SERVER LISTENER
// WILL TELL OUR APP TO LISTEN FOR REQUESTS
// ON A CERTAIN PORT
// *****************************
// app.listen(PORT, FUNCTION)
// The function will run after the server turns on
app.listen(3000, () => {console.log("server is listening on port 3000")})

boiled down

const express = require("express")


const app = express()


app.get("/", (req, res) => {
    res.send("<h1>Hello World</h1>")
})


app.listen(3000, () => {console.log("server is listening on port 3000")})

properties of req

• req.query: object with query params ?key=value&key=value
• req.params: object with url params /url/:param
• req.url: url of the request
• req.method: method of the request
• req.headers: object of request headers
• req.body: object with request body data

properties of res

• res.send() sends a response as html, json or text depends on what is passed

• res.render() will render a view in a "views" folder using a templating library matching the file extension (.ejs). Can send data as a second argument to be used when rendering the view.

• res.json() will respond with json

Middleware

built into express

• app.use(express.urlencoded({extended: true}): parses urlencoded bodies from traditional form submissions into req.body
• app.use(express.json(): parses json bodies from AJAX/Fetch requests into req.body
• app.use(express.static("public"): Creates a static server out a folder called "public"

3rd party middleware

middleware	install	purpose
app.use(cors())	npm install cors	set cors headers to allow cross origin requests
app.use(methodOverride("_method"))	npm install method-override	allow overiding of method for form posts requests into put or delete using URL query xyz.com/something?_method=DELETE
app.use(morgan('dev'))	npm install morgan	log details about each incoming request for troubleshooting
app.use(session({secret: "cat"})	npm install express-session	For persisting session cookies to save data between requests
app.use(cookieParser())	npm install cookie-parser	For parsing incoming cookies into req.cookie