Node.js - Kyle Hovey¶
Introduction¶
What is Node.js?¶
JavaScript is a programming language that is used within web browsers to manipulate webpages. Normally JavaScript operates within a browser, but what if JavaScript could be used outside of a browser? That is what Node.js enables it to do.
One confusing thing is what Node.js actually is. It is not a programming language in itself. Rather it is a program that runs the programming language JavaScript. The Node.js software is actually written in the language C. Using C as the structure of the Node progam gives the program the capability of networking, which would not be possible if Node itself was written in JavaScript. Node not only provides the program to run JavaScript, but provides a JavaScript library that greatly enhances the capabilities of the language. Before getting too much into the details of Node.js, here is a guide to getting it set up and testing the installation. [org]
Installing Node.js¶
This short tutorial will help to install Node.js and write a "Hello, World!" program to test your installation. The first thing that needs to be done is downloading Node.js from the Node.js Website
Testing Installation: Hello, world!¶
Once the install is complete create a new document called main.js. No need for an IDE or anything, just use a basic text editor such as sublime. Copy the following code into the file
/* Hello world program in node.js */
console.log("Hello, world!")
This is just like a normal Javascript file, the difference is that
the node.js module is used to execute it. To test the installation open the
command prompt and navigate to the directory where main.js is saved. Then type
node main.js and hit enter. "Hello, World!" should appear. [tut]
History of Node.js¶
Node.js was started by Ryan Dahl and a team of other developers that worked for a company named Joyent. The first release in 2009 only supported Linux, but since then Node.js has been expanded to be cross platform, supporting OS X, Microsoft Windows, and Linux. Node.js is now under the care of The Node.js Foundation which guides the development and release of Node.js. [bhn]
Why use Node.js?¶
Alright, so you can write and run JavaScript code without a browser. What's the point? One of the most common uses of Node.js is server side programming. The JavaScript libraries that are provided by Node.js give it this capability. Node.js gives developers the opportunity to develop not only the frontend using JavaScript, but the backend of their websites in as well. This means that it is not necessary to learn another language to use on the backend such as Java or PHP.
Another benifit of using JavaScript on the frontend and backend is that no longer a need for the translation of data. When using different languages A translator, such as JSON is used to change the format of the data when sending and receiving it from the server. Using a translator like JSON can pose an issue because it needs to be able to support the data type that you are using, and that just adds one more layer of potential problems that could be avoided altogether by using Node.js. [win]
Running a File Server with Node.js¶
Node.js is made to be run on a server. One operation of a server is to serve
files to the user. This is incredibly easy to do with Node.js. Copy the
following code into an empty file with the title NodeFileServer.js.
var sys = require("util"),
http = require("http"),
url = require("url"),
path = require("path"),
fs = require("fs");
http.createServer(function(request, response) {
var uri = url.parse(request.url).pathname;
var filename = path.join(process.cwd(), uri);
fs.exists(filename, function(exists) {
if(!exists) {
response.writeHead(404, {"Content-Type": "text/plain"});
response.end("404 Not Foundn");
return;
}
fs.readFile(filename, "binary", function(err, file) {
if(err) {
response.writeHead(500, {"Content-Type": "text/plain"});
response.end(err + "n");
return;
}
response.writeHead(200);
response.end(file, "binary");
});
});
}).listen(8080);
console.log("Server running at http://localhost:8080/");
Then place this picture in the same directory.
After saving these two things navigate to the directory that these are saved in
on the command-line and type node NodeFileServer.js. After that executes
find a browser and go to http://localhost:8080/nodejslogo.jpg. The following
screen should appear.
It is that easy to create a file server with Node.js! But what exactly is happening? [win]
How Does Node.js Work?¶
The code is executed using Google Chrome's V8 JavaScript Engine, and that helps Node.js execute code very efficiently. This, however, is not the only feature of Node.js that make it a good choice for building applications. Node.js is also single threaded, but the non-blocking nature of Node.js (which will be explained in a later section) enables it to serve a much larger number of requests than traditional servers. Node.js uses what is called asynchronous event-driven, non-blocking runtime. There is obviously a lot of explaination for that phrase to make any sense to the average listener, so the next few sections will hopefully provide some clarity. [org]
Asynchronous Event-Driven Programming¶
Asynchronous programming is something that is not often talked about, but is used by almost every programmer. Asynchronous programs are responsive to the user. In web development this makes a lot of sense. There is no need for a webpage to ask "Did anything happen?" repeatedly. Instead the webpage reacts to what are called events. On a webpage a user clicks a button, and an event is fired. Then the code that is attached to that event runs. It isn't possible to see what order the code will be executed in when looking at the source. In the above example the file server only provides files at the users request. When a user requests a file an event is triggered, and the server retrieves the file. The rest of the time the node is inactive. [sin]
Non-Blocking¶
Node.js is designed to be non-blocking, but what exactly does this mean? In plain english it means that the program doesn't have to wait for one thing to finish before it can move on to the next thing. This specifically applies to non-JavaScript operations when using Node.js. In the above example, if another function was added to the program then that function would not have to wait for the program to retrieve the file before it could execute. This feature, combined with asynchronous event-driven programming makes Node.js really fast. Speed is one of the major advantages of Node.js. [tut]
Using Javascript to program¶
It is also possible with Node.js to run programs that would typically be written
in other languages. This next example shows how advanced these programs can be.
It outputs CIS in ASCII characters with a user specified font size. This is done
using while loops, nested for loops, and if else statements in order to show
that these programs can be just as complex as programs written in other
languages. Place this code in a file named PrintCIS.js and run in from the
command-line by entering node PrintCIS.js
var stdin = process.openStdin();
stdin.addListener("data", function(d) {
// note: d is an object, and when converted to a string it will
// end with a linefeed. so we (rather crudely) account for that
// with toString() and then trim()
var scale = Number(d.toString().trim());
var c1 = ["C", "C", "C", "C", "C"];
var c2 = ["C", " ", " ", " ", " "];
var i1 = ["I", "I", "I", "I", "I"];
var i2 = [" ", " ", "I", " ", " "];
var s1 = ["S", "S", "S", "S", "S"];
var s2 = ["S", " ", " ", " ", " "];
var s3 = [" ", " ", " ", " ", "S"];
var count = 0;
var line = 1;
var output = "";
while (line <= 5*scale)
{
if (line == ((scale*5) - (scale - 1)) || line == 1){
for (var i = 0; i < scale; i++) {
for (var j = 0; j < c1.length; j++) {
count = 0;
while(count < scale)
{
output += c1[j];
count++;
}
}
output += "\n";
line++;
}
}
else
{
for (var i = 0; i < c2.length; i++)
{
count = 0;
while (count < (scale))
{
output+=c2[i];
count++;
}
}
output += "\n";
line++;
}
}
line = 1;
output += "\n";
while (line <= (5*scale))
{
if (line == ((scale*5) - (scale - 1)) || line == 1)
{
for (var j = 0; j < scale; j++)
{
for (var i = 0; i < i1.length; i++)
{
count = 0;
while (count < (scale))
{
output += i1[i];
count++;
}
}
output += "\n";
line++;
}
}
else
{
for (var i = 0; i < i2.length; i++)
{
count = 0;
while (count < (scale))
{
output += i2[i];
count++;
}
}
output += "\n";
line++;
}
}
line = 1;
output += "\n";
while (line <= 5*scale)
{
if (line == ((scale*5) - (scale - 1)) || line == 1 || line == (scale*2) + 1)
{
for (var j = 0; j < scale; j++)
{
for (var i = 0; i < s1.length; i++)
{
count = 0;
while (count < (scale))
{
output += s1[i];
count++;
}
}
output += "\n";
line++;
}
}
else if (line < (scale*2) + 1 && line > 1)
{
for (var i = 0; i < s2.length; i++)
{
count = 0;
while (count < (scale))
{
output += s2[i];
count++;
}
}
output += "\n";
line++;
}
else
{
for (var i = 0; i < s3.length; i++)
{
count = 0;
while (count < (scale))
{
output += s3[i];
count++;
}
}
output += "\n";
line++;
}
}
console.log(output);
});
Nothing happened? Type a number into the command prompt and hit Enter.
Enter any font size and watch the letters get bigger! This example shows that by using Node.js, JavaScript can be used to make applications that take and process input just the same as any other programming language. This is only one example of what can be done with JavaScript. Experimentation is encouraged in order to learn all the capabilities of JavaScript using Node.js.
Other Features of Node.js¶
As mentioned previously, Node.js also provides a library that makes programming in JavaScript easier to program with, and also adds features to the language.
One of these additions is the introduction of global objects. This includes
__filename and __dirname, which can be printed to show the file path and
directory that the file is located in, respectively. There are also three Global
functions. setTimeout() can be used to run a callback after a certain number
of milliseconds. clearTimeout() is used to clear a previously set timer. The
last is setInterval() which can be used to run a function repeatedly after
a specified number of milliseconds.
Another feature of Node.js is the modules that it provides. One of these is the HTTP Module, which was used in the second example above. The HTTP module makes it possible to create a web server and client with JavaScript. Node.js also comes equipped with several utility modules. The uses of these modules vary. The OS Module provides functions that are related to operating-systems. There is the Path Module, which adds the capability of handling and transforming file paths. The Net Module acts as a network wrapper. A module called the DNS Module makes DNS lookup possible with JavaScript functions. Finally the Domain Module allows the handling of multiple I/O operations in one group. [tut]
Conclusion¶
Node.js expands the usefulness of JavaScript in many ways. Whether it is on the server, or to write an application in JavaScript, Node.js provides this capability. While there is a bit of a learning curve to understand the libraries added to JavaScript by Node.js, asynchronous, and non-blocking methods of programming, once these are understood Node.js can be utilized to make extremely fast applications. Node.js simplifies programming with JavaScript, as well as networking applications as a whole. Node.js is still a fairly new technology and is being tweaked and improved constantly.
| [win] | (1, 2) Brett McLaughlin "What is Node.js?." O'Reilly, 06 Jul. 2011. Web. 22 Apr. 2017. |
| [org] | (1, 2) Erty Seidel "What are Javascript, AJAX, jQuery, AngularJS, and Node.js?." Organic Donut, 07 Aug. 2013. Web. 22 Apr. 2017. |
| [bhn] | Shailendra Chauhan "Brief history of node.js and io.js." DotNetTricks, 07 Sep. 2016. Web. 22 Apr. 2017. |
| [sin] | Chris Tavares "Why is Node.js single threaded?." StackOverflow, 21 Dec. 2013. Web. 22 Apr. 2017. |
| [tut] | (1, 2, 3) "Node.js Tutorial." Tutorialspoint, 2017. Web. 22 Apr. 2017. |