6 1 hello world example tủ tài liệu training pdf

Hello World ExampleIn this chapter, to help you get your feet wet using Express.js, we’ll build the quintessential programming example—the Hello World app.. The topics covered in this ch

Hello World Example

Hello World Example

In this chapter, to help you get your feet wet using Express.js, we’ll build the

quintessential programming example—the Hello World app If you’ve already built some variation of this Express.js app (perhaps by following an online tutorial), feel free to skip to the next chapter and go either to Chapter 3 for the API methods and objects, or to Chapter 19-22 for examples The topics covered in this chapter are as follow:

● Getting started: creating the minimal Express.js app from scratch

● Generator commands: command-line options of Express.js Generator

● MVC structure and modules: a common way to organize code for Express.js apps

● Watching for file changes: a development tip

Hello World Example

Getting Started

I’ve always liked the bottom-up approach to teaching, starting from the most basic concepts and progressing toward more complex ones Also, I’ve noticed that

developers gain more confidence when they learn how to create something from scratch instead of just modifying an existing project or using boilerplate

To begin, you’ll write a web server that runs locally on port 3000 So, when you open the http://localhost:3000 location in the browser, you should see Hello World The number 3000 is the de-facto standard port number for Express.js applications

Hello World Example

The file hello.js server will utilize Express.js; therefore, let’s include this library:

var express = require('express');

Now we can create an application (i.e., instantiate an Express.js object):

var app = express();

The web server will run locally on port 3000, so let’s define it here: var port = 3000; Next, let’s define a wildcard route (*) with the app.get() function:

app.get('*', function(request, response){

resquest.end('Hello World');

});

Hello World Example

The app.get() function accepts regular expressions3 of the URL patterns in a

string format In our example, we’re processing all URLs by specifying the wildcard

* character

In the case of Express.js, you can use RegExps in routes to define complex URL patterns dynamically To find out more about regular expressions, check out the documentation at https://developer.mozilla.org/en-US/docs/

Web/JavaScript/Guide/Regular_Expressions

Using Request Handlers

The second parameter to the app.get() method is a request handler A typical

Express.js request handler is similar to the one we pass as a callback to the

native/core Node.js http.createServer() method For those unfamiliar with the core http module, a request handler is a function that will be executed every time the server receives a particular request, usually defined by an HTTP method (e.g., GET) and the URL path (i.e., the URL without the protocol, host, and port) The Express.js request handler needs at least two parameters—request, or simply req, and response, or res (more on this later in Chapter 9) Similarly to their core

counterparts, we can utilize readable and writable streams interfaces

(http://nodejs.org/api/stream.html) via response.pipe() and/or response.on('data', function(chunk) { })

Outputting Terminal Messages

Finally, we start the Express.js web server and output a user-friendly terminal

message in a callback: app.listen(port, function(){ console.log('The server is

running, ' + ' please, open your browser at http://localhost:%s', port); }); To run the script, we execute $ node hello.js from the project folder You should see “The server is running, please open your browser at http://localhost:3000

Now, if you open your browser at http://localhost:3000 (same as

http://127.0.0.1:3000, http://0.0.0.0:3000, or http://localhost:3000/), you should see the Hello World message no matter what the URL path is (see Figure 2-2) The URL path is the string after the domain and port, so for http://localhost:3000/, it is / and for http://localhost:3000/messages/ is it “/messages/” When you use “*” in the route definition, this path doesn’t matter

Full Code

The full code of the hello.js file is provided here for your reference:

var express = require('express');

var port = 3000;

var app = express();

app.get('*', function(request, response){

resquest.end('Hello World');

});

app.listen(port, function(){

console.log('The server is running, ' + ' please open your browser at http://localhost:%s', port); });

Enhancing the App

Enhancing the App We can make our example a bit more interactive by echoing the name that

we provide to the server along with the “Hello” phrase To do so, we can copy the hello.js file with $ cp hello.js hello-name.js and add the following route right before the all-encompassing route (all.get('*', )) from the previous example:

app.get('/name/:user_name', function(req,res) {

res.status(200);

res.set('Content-type', 'text/html');

res.send('' + 'Hello ' + req.params.user_name + '' + '' ); });

Inside of the /name/:name_route route, we set the proper HTTP status code (200 means OK) and HTTP response headers and wrap our dynamic text in HTML body and h1 tags.

The full source code of the hello-name.js file is provided next (and is also available in the downloadable source code for this book):

var express = require('express');

var port = 3000;

var app = express();

app.get('/name/:user_name', function(request,response) {

response.status(200); response.set('Content-Type', 'text/html');

response.end('' + 'Hello ' + req.params.user_name + '' + '' );

});

app.get('*', function(request, response){

response.end('Hello World');

});

app.listen(port, function(){

console.log('The server is running, ' + ' please open your browser at http://localhost:%s', port);

});

After shutting down the previous server and launching the hello-name.js script, you’ll be able to see the dynamic response; for example, entering

http://localhost:3000/name/azat in your browser

So far we’ve created two Express.js apps from scratch Each of them was just a few lines of code This should give you the confidence, and illustrate how easy it

is, to create web servers with Express.js and Node.js! But there’s an even faster way—Express.js generator Let’s cover its commands and options