Express Cheatsheet

A quick reference cheatsheet for Express, a flexible and streamlined web framework for Node.js

Getting Started

Hello World

"Create project, add package.json configuration

$ mkdir myapp # create directory
$ cd myapp    # enter the directory
$ npm init -y # Initialize a configuration

Install dependencies
```
$ npm install express
```

Entry file index.js add code:

const express = require("express");
const app = express();
const port = 3000;
app.get("/", (req, res) => {
  res.send("Hello World!");
});
app.listen(port, () => {
  console.log(`Listening port on ${port}`);
});

Run the application using the following command
```
$ node index.js
```

express -h

Usage: express [options] [dir]
Options:
  -h, --help output usage information
      --version output version number
  -e, --ejs add ejs engine support
      --hbs add hbs engine support
      --pug add pug engine support
  -H, --hogan add hogan.js engine support
      --no-view No view engine generated
  -v, --view <engine> add view <engine> support (ejs|hbs|hjs|jade|pug|twig|vash) (default jade)
  -c, --css <engine> add stylesheet <engine> support (less|stylus|compass|sass) (default css)
      --git add .gitignore
  -f, --force force non-empty directories

Create a myapp project

$ express --view=pug myapp
# run the application
$ DEBUG=myapp:*npm start

express()

`express.json()`	#
`express.raw()`	#
`express.Router()`	#
`express.static()`	#
`express.text()`	#
`express.urlencoded()`	#

Router

`router.all()`	#
`router.METHOD()`	#
`router.param()`	#
`router.route()`	#
`router.use()`	#

Application

var express = require("express");
var app = express();

console.dir(app.locals.title);
//=> 'My App'
console.dir(app.locals.email);
//=> 'me@myapp.com'

Attribute

`app.locals`	Local variables in the application #
`app.mountpath`	Path pattern for mounting sub-apps #

Events

mount

The child application is mounted on the parent application, and the event is triggered on the child application #

Method

`app.all()`	#
`app.delete()`	#
`app.disable()`	#
`app.disabled()`	#
`app.enable()`	#
`app.enabled()`	#
`app.engine()`	#
`app.get(name)`	#
`app.get(path, callback)`	#
`app.listen()`	#
`app.METHOD()`	#
`app.param()`	#
`app.path()`	#
`app.post()`	#
`app.put()`	#
`app.render()`	#
`app.route()`	#
`app.set()`	#
`app.use()`	#

Request

Attribute

`req.app`	#
`req.baseUrl`	#
`req.body`	#
`req.cookies`	#
`req.fresh`	#
`req.hostname`	#
`req.ip`	#
`req.ips`	#
`req.method`	#
`req.originalUrl`	#
`req.params`	#
`req.path`	#
`req.protocol`	#
`req.query`	#
`req.route`	#
`req.secure`	#
`req.signedCookies`	#
`req.stale`	#
`req.subdomains`	#
`req.xhr`	#

Method

`req.accepts()`	#
`req.acceptsCharsets()`	#
`req.acceptsEncodings()`	#
`req.acceptsLanguages()`	#
`req.get()`	Get HTTP request header fields #
`req.is()`	#
`req.param()`	#
`req.range()`	#

Response

app.get("/", function (req, res) {
  console.dir(res.headersSent); //false
  res.send("OK");
  console.dir(res.headersSent); //true
});

Attribute

`res.app`	#
`res.headersSent`	#
`res.locals`	#

Method

`res.append()`	#
`res.attachment()`	#
`res.cookie()`	#
`res.clearCookie()`	#
`res.download()`	Prompt for files to download #
`res.end()`	end the response process #
`res.format()`	#
`res.get()`	#
`res.json()`	Send JSON response #
`res.jsonp()`	Send a response with JSONP support #
`res.links()`	#
`res.location()`	#
`res.redirect()`	Redirect request #
`res.render()`	render view template #
`res.send()`	Send various types of responses #
`res.sendFile()`	Send a file as an octet stream #
`res.sendStatus()`	#
`res.set()`	#
`res.status()`	#
`res.type()`	#
`res.vary()`	#

Example

Router

Called for any request passed to this router

router.use(function (req, res, next) {
  //.. some logic here .. like any other middleware
  next();
});

will handle any request ending in /events

//depends on where the router "use()"
router.get("/events", (req, res, next) => {
  //..
});

Response

The res object represents the HTTP response sent by the Express application when it receives an HTTP request

app.get("/user/:id", (req, res) => {
  res.send("user" + req.params.id);
});

Request

A req object represents an HTTP request and has properties for the request query string, parameters, body, HTTP headers, etc.

app.get("/user/:id", (req, res) => {
  res.send("user" + req.params.id);
});

res. end()

res.end();
res.status(404).end();

End the response process. This method actually comes from the Node core, specifically the response.end() method of http.ServerResponse

res.json([body])

res.json(null);
res.json({ user: "tobi" });
res.status(500).json({ error: "message" });

app.all

app.all("/secret", function (req, res, next) {
  console.log("access secret section...");
  next(); // Pass control to the next handler
});

app.delete

app.delete("/", function (req, res) {
  res.send("DELETE request to homepage");
});

app.disable(name)

app.disable("trust proxy");
app.get("trust proxy");
// => false

app.disabled(name)

app.disabled("trust proxy");
// => true

app.enable("trust proxy");
app.disabled("trust proxy");
// => false

app.engine(ext, callback)

var engines = require("consolidate");

app.engine("haml", engines.haml);
app.engine("html", engines.hogan);

app.listen([port[, host[, backlog]]][, callback])

var express = require("express");

var app = express();
app.listen(3000);

Routing

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

//Respond to "hello world" when making a GET request to the homepage
app.get("/", (req, res) => {
  res.send("hello world");
});

// GET method routing
app.get("/", (req, res) => {
  res.send("GET request to the homepage");
});

// POST method routing
app.post("/", (req, res) => {
  res.send("POST request to the homepage");
});

Middleware

function logOriginalUrl(req, res, next) {
  console.log("ReqURL:", req.originalUrl);
  next();
}

function logMethod(req, res, next) {
  console.log("Request Type:", req.method);
  next();
}

const log = [logOriginalUrl, logMethod];

app.get("/user/:id", log, (req, res, next) => {
  res.send("User Info");
});

Using templates

app.set("view engine", "pug");

Create a Pug template file named index.pug in the views directory with the following content

html
  the head
    title= title
  the body
    h1=message

Create a route to render the index.pug file. If the view engine property is not set, the extension of the view file must be specified

app.get("/", (req, res) => {
  res.render("index", {
    title: "Hey",
    message: "Hello there!",
  });
});

Adapted from Fechin/reference GPL-3.0 license Markdown source Changes and attribution