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Introduction to Node.js Part I - Node.js Overview

Node.js, JavaScript, intermediate, tutorial, intro-to-node-js8 min read

Introduction

Welcome to the first part of the six-part Introduction to Node.js tutorial series. By the end of this tutorial, you will:

  • Be able to explain what Node.js is and how it's different from the browser
  • Understand the difference betweeen blocking versus non-blocking patterns in Node.js
  • Use the Node.js REPL environment
  • Use basic Node.js debugging tools

Tutorial Outline

  • Node.js Overview
    • What is Node.js?
    • Node.js Uses the V8 JavaScript Engine
    • Node.js versus the Browser
    • Node.js Motivation
      • Blocking Code
      • Non-Blocking Code
      • Non-Blocking Code Benefits
      • Node.js Case Studies
  • Exploring the Node.js REPL Environment
  • Setup Course Folder & Test File
  • Debugging Node.js Applications Effectively
  • Debugging with an Integrated Development Environment (IDE)
  • Debugging with Chrome DevTools
  • Additional Resources
  • Review
  • Key Takeaways
  • What's next

Node.js Overview

What is Node.js?

According to the official website,

1Node.js® is a JavaScript runtime built on Chrome's V8 JavaScript engine.

Node.js enables JavaScript to run outside of the browser. It can be used to build server-side applications that can handle high traffic volumes efficiently.

Node.js is portable, meaning it can run on a variety of operating systems, including Mac, Windows, Linux and several other systems. It is also a free and open-sourced technology.

Node.js was first released in 2009 by a programmer named Ryan Dahl.

Node.js uses the V8 JavaScript Engine

A JavaScript Engine is a program that compiles JavaScript to machine code that the operating system can understand.

V8 is the name of the JavaScript Engine that powers Node.js. Created by Google and open-sourced since 2008, V8 powers the Google Chrome browser today. It is written in C++.

One benefit of using Node.js is that it benefits from Google's investment in V8's improved performance year after year.

Besides V8, examples of other JavaScript Engines include SpiderMonkey(Firefox) and Chakra(Edge).

Node.js versus the Browser

Before the advent of Node.js, JavaScript could only run in the browser, and its primary purpose was to create browser interactions (e.g., adding click events). Node.js allows us to write JavaScript in the server to perform common server tasks, such as accessing the file system and connecting to databases.

However, while Node.js and browsers like Chrome both execute Javascript and use the same V8 JavaScript engine, there are a few key differences between them:

BrowserNode.js
Access to document and window objectsAccess to http, fs objects
global object references the windowglobal object references Node.js-specific modules
Uses ECMAScript modules (i.e., import,export)Uses the CommonJS module system (i.e., require(), module.exports)

Nowadays, JavaScript has proven to be among one of the most popular programming languages. If you're a developer who extensively uses Javascript, then Node.js offers a huge advantage - which is the ability to program your entire application - frontend and backend - in a single language.

However, while Node.js and browsers like Chrome both execute Javascript and use the same V8 JavaScript engine, there are a few key differences between them:

  • While Node.js and browsers share several common built-in JavaScript features (e.g., Array), there are several predefined objects that exist in one environment but not in the other. For example, Node.js does not have access to the document and window objects, which are used on the client-side for Document Object Model (DOM) manipulation and user event handling. The browser, on the other hand, does not have access to Node.js API's such as http and fs, which are needed for setting up web servers and manipulating file systems, respectively.

  • Both have access to a global object. In the browser, the global object references the window object. In Node.js, however, the global object exposes a collection of useful modules, functions, and strings that we can use in our programs.

  • Node.js uses the CommonJS module system, which uses require() and module.exports, to share code between different files. In the browser, we are starting to see the ECMAScript modules standard, which uses the import and export statements, being implemented. As of October 2020, ECMAScript modules is still an experimental feature only in Node.js.

Node.js Motivation

Prior to the release of Node.js, there were major issues with popular servers, such as the Apache HTTP server, at that time that made it difficult to create scalable applications.

For example, the Apache HTTP server had trouble handling a high volume of concurrent requests. It would create a separate thread for each network request, which led to tremendous resources being consumed during periods of high website traffic. An increase in traffic beyond the server's capacity would cause Apache to start dropping additional requests, leading to a poor customer experience.

The Apache HTTP server also implemented "blocking code", which meant a program had to wait for a current task to finish and release its resources before the program could proceed with the next task.

Node.js was created to solve these problems.

Blocking Code

To understand why Node.js is an excellent choice for creating scalable network applications, we must first understand blocking and non-blocking code as they relate to Node.js' I/O operations.

I/O stands for input/output, which is needed whenever a Node.js app is communicating with the server it's running on (e.g., reading some data from a file on the file system) or some other server (e.g., querying the database, reading from the network).

Blocking methods execute synchronously. Suppose an application has the following code to read a file:

1// Load the file system module
2const fs = require("fs");
3
4// While waiting for the file to be read, can't do anything else!
5const data = fs.readFileSync("/file.md", "utf-8");
6console.log(data);
7
8// Will only run after the console.log on the previous line
9doMoreStuff();

The example above is synchronous.

const data = fs.readFileSync("/file.md", "utf-8"); will block the execution of any additional JavaScript (e.g., doMoreStuff()) until the entire /file.md file is read.

If an error is thrown, it will need to be caught or the process will crash.

While separate threads could be used to handle multiple tasks concurrently, spawning a new thread for each task is expensive in terms of memory and CPU usage. As number of threads increase, so does memory usage. Multi-threaded applications also result in increased complexity (e.g., multiple threads accessing shared data)

Enter non-blocking code.

Non-Blocking Code

Non-blocking methods execute asynchronously.

And here is the asynchronous version of the file read operation from the previous section:

1// Load the file system module
2const fs = require("fs");
3
4// Pass a callback function as a third argument
5fs.readFile("/file.md", "utf-8", (err, data) => {
6 if (err) throw err;
7 console.log(data);
8});
9
10// Will run before console.log
11doMoreStuff();

In the asynchronous version,

  • fs.readFile() is non-blocking so JavaScript execution can continue and doMoreStuff() will be called before fs.readFile() has finished running
  • You can pass a callback as a third argument to fs.readFile(). During program execution, this callback function gets sent to a callback queue; the callback function only gets invoked when the file read is finished.
    • This ability to register a callback in an asynchronous call is what makes Node.js event-driven.
    • You can handle any errors in this callback; the first argument of this callback gives us access to the error object (i.e., error-first callback).

How does JavaScript know to run a callback function asynchronously?

Because of something running behind the scenes called the Event Loop!

A detailed discussion of the Event Loop is outside the scope of this tutorial, but here's an excellent video about the event loop.

This mechanism helps the program invoke the callback function when the main function has finished function.

The Event Loop is neither part of the V8 JavaScript Engine nor is it part of the JavaScript language. It is implemented by a library called libuv within Node.js.

Non-Blocking Code Benefits

Non-blocking paradigms allow Node.js to process other code or make other requests while waiting for a response from some long-running operations (e.g., network requests).

A Node.js app is capable of handling higher throughput and thousands of concurrent connections while processing multiple requests at the same time in a single thread, without having to create a new thread for every request.

For this reason, Node.js libraries are normally created using non-blocking paradigms.

However, Node.js is not a suitable choice for CPU-intensive and heavy computing workloads (e.g., video transcoding, graphics processing, sort a billion users), since CPU tasks are not executed asynchronously and will block the single Node.js thread, causing the application to be unresponsive.

Node.js Case Studies

Here are a few case studies of how different companies have used Node.js to scale their applications:

Exploring the Node.js REPL Environment

When Node.js is installed, you'll have access to the node executable program in the terminal.

  1. Open up your terminal.

  2. Type node into your terminal. This will open up a REPL or Read-Evaluate-Print-Loop where we can run individual node statements using JavaScript. The command stays in idle mode, waiting for us to input code.

  3. Core JavaScript features we're familiar with in the browser like toUpperCase() are still available in Node.js. Try running the following with REPL:

    1"hello world".toUpperCase(); // returns 'HELLO WORLD'
  4. Try entering the name of a JavaScript class, like Number, add a dot and press tab. The REPL will print all the properties and methods you can access on that class. Try running some of these methods and properties (e.g., Number.MAX_VALUE).

  5. Inspect the global objects you have access to by typing global. and pressing tab. What do you see? Which of these global objects are you familiar with from browser-based JavaScript?

  6. To exit REPL mode, simply type .exit or hit CTRL + c twice.

Setup Course Folder & Test File

Create a folder where you will save your work for this course.

You can call this folder intro-to-nodejs-course.

  1. Navigate to your home directory:

    1$ cd ~
  2. Create a new folder called intro-to-nodejs-course and change into it:

    1$ mkdir intro-to-nodejs-course
    2$ cd intro-to-nodejs-course
  3. Create a script file in your course directory:

    1$ touch script.js
  4. Add a console.log message to the script.js file:

    script.js
    1console.log("hello world");
  5. Run the script from terminal:

    1$ node script.js

What do you see?

Debugging Node.js Applications Effectively

Many developers use console.log to debug their Node.js applications. This technique is great for dumping a variable to the terminal so you can check its value or figuring out what order your code is running in. However, it is not really the best option.

Using console.log to debug your code generally slows down the development process, as you'd have to repeatedly stop your app, insert a console.log, and start your app again. Also, it complicates the debugging process as you're trying to log out the values you're debugging amidst the noise of other logging operations.

Debugging with an Integrated Development Environment (IDE)

VSCode makes it really easy to start a debugging environment for our Node.js application! Let's take a look at an example.

  1. In your script.js, add the following code:

    script.js
    1let count = 5;
    2// the setInterval() function invokes the callback every 1000 milliseconds
    3const countDown = setInterval(() => {
    4 console.log(`counting down ${count}`);
    5 count--;
    6
    7 if (count < 0) {
    8 console.log("Time's up!");
    9
    10 // clears the timer when the count is negative
    11 clearInterval(countDown);
    12 }
    13}, 1000);
  2. If you're using VSCode, hit Command + Shift + D to launch the debugger. Select Node.js as the environment. Set a breakpoint by clicking to the left of the count-- line.

    Setting a breakpoint in VSCode debugger

  3. Next, press the Run and debug button on the left side of the window. The application automatically stops at the breakpoint you just set. You can start stepping through the code to observe how the count variable changes during code execution!

Debugging with Chrome DevTools

Developers often use the Chrome DevTools to debug client-side JavaScript code. Since Chrome and Node.js share the same V8 JavaScript engine, it is also possible to use the Chrome DevTools for debugging and profiling your applications.

Chrome DevTools gives you access to the profiler, stack visualization information, code navigation features, and a very cool debugger. A debugger is automatically bundled with your Node.js installation.

  1. Attach Chrome DevTools to a Node.js instance for debugging! Open your terminal and run

    1$ node --inspect-brk script.js
  2. Then in Chrome type this URL: chrome://inspect.

  3. Click the inspect link next to the Node target, and you’ll have access to Node.js in the browser DevTools. You can now insert breakpoints and step through the code!

Additional Resources:

Review

Take a moment to reflect on what you’ve learned in this tutorial and answer the following questions:

  • What is Node.js?
  • What is V8?
  • What is blocking code? What is non-blocking code? Which pattern allows Node.js to be highly performant?
  • What are the differences and similarities between Node.js and the browser?

Key takeaways

  • Node.js is a JavaScript runtime that enables JavaScript to run outside of the browser. It is built on Chrome's V8 JavaScript engine.

  • V8 is the name of the JS Engine that powers Node.js. It was created by Google and currently powers Google Chrome.

  • Blocking code executes synchronously, or one line after the after. Non-blocking code executes asynchronously, so JavaScript execution can continue while an earlier task is ongoing. Non-blocking paradigms allow Node.js to process other code or make other requests while waiting for a response from some long-running operations (e.g., network requests).

  • While Node.js and browsers share several common built-in JavaScript features (e.g., Array), there are several predefined objects that exist in one environment but not in the other. For example, Node.js does not have access to the document and window objects that are available in the browser. While both have access to a global object, in the browser, the global object references the window object. In Node.js, however, the global object exposes a collection of useful modules, functions, and strings that we can use in our programs.

What’s next?

Now that you understand the basics of working within the Node.js environment, it’s time to learn about Node's built-in libraries. In Part 2, you’ll learn how to access and interact with the file system and Node.js processes using special Node.js packages.

Continue to Part 2

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