8751. Getting Started with Express
Express

Introduce how to setup web server with express in Node.js.

1. What is Express?

Express is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. It is the standard web server framework for Node.js. Some notes of this posting comes from the book - Express in Action.

1.1 Hello World

A standard way to setup web server with express.

// helloworld.js
// Requires Express and puts it in a variable
var express = require("express");
// Calls express() and puts new Express application inside the app variable
var app = express();

// Sends “Hello, world!”
app.get("/", function(request, response) {
  response.send("Hello, world!");
});

//Starts the Express server on port 3000 and logs that it has started
app.listen(3000, function() {
  console.log("Express app started on port 3000.");
});

image

2. Express Core

Express has four major features:

  • Middleware: An array of functions to process incoming requests.
  • Routing: Rules how an application’s endpoints (URIs) respond to client requests.
  • Extensions: Extends the request and response objects with extra methods and properties.
  • Views: Dynamically render HTML at server side.

3. Web Server

3.1 Node Http Module

Actually, we can create web server with node http module without using express.

// httpserver.js
var http = require("http");

function requestHandler(request, response) {
  console.log("In comes a request to: " + request.url);
  response.end("Hello, world(http)!");
}

var server = http.createServer(requestHandler);
server.listen(3000, function() {
  console.log("Web server(http) started on port 3000.");
});

3.2 Http + Express

// httpexpress.js
var express = require("express");
var http = require("http");
var app = express();

app.use(function(request, response) {
  console.log("In comes a request to: " + request.url);
  response.end("Hello, world(http+express)!");
});

http.createServer(app).listen(3000, function() {
  console.log("Web server(http+express) started on port 3000.");
});

3.3 Express Only

// expressserver.js
var express = require("express");
var app = express();

app.use(function(request, response) {
  console.log("In comes a request to: " + request.url);
  response.end("Hello, world(express)!");
});

app.listen(3000, function() {
  console.log("Web server(express) started on port 3000.");
});

4. Other Usage

1) Enable CORS

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  res.header("Access-Control-Allow-Methods", "*");
  next();
});

2) Query arguments, /search?q=javascript

app.get("/search", function(req, res) {
    req.query.q == "best restaurant"
// ...
});

3) Redirect

response.redirect("/hello/world");
response.redirect("http://expressjs.com");

4) Https

// https
var express = require("express");
var https = require("https");
var fs = require("fs");
var app = express();
// ... define your app ...
var httpsOptions = {
  key: fs.readFileSync("path/to/private/key.pem"),
  cert: fs.readFileSync("path/to/certificate.pem")
};
https.createServer(httpsOptions, app).listen(3000);

5) Run both an HTTP server and an HTTPS server.

var express = require("express");
var http = require("http");
var https = require("https");
var fs = require("fs");
var app = express();
// ... define your app ...
var httpsOptions = {
  key: fs.readFileSync("path/to/private/key.pem"),
  cert: fs.readFileSync("path/to/certificate.pem")
};
http.createServer(app).listen(80);
https.createServer(httpsOptions, app).listen(443)

6) Debugging Express
To see all the internal logs used in Express, set the DEBUG environment variable to express:* when launching your app.

"debug": "DEBUG=express:* node helloworld.js"

Run ‘npm run debug’. image

5. Source Files

6. Reference