Debugging JavaScript with the Node Debugger

Debugging JavaScript with the Node Debugger

Debugging JavaScript with the Node Debugger: The Node debugger command line is a useful tool.

It’s a trap! You’ve spent a good amount of time making changes, nothing works. Perusing through the code shows no signs of errors. You go over the logic once, twice or thrice, and run it a few times more. Even unit tests can’t save you now, they too are failing. This feels like staring at an empty void without knowing what to do. You feel alone, in the dark, and starting to get pretty angry.

A natural response is to throw code quality out and litter everything that gets in the way. This means sprinkling a few print lines here and there and hope something works. This is shooting in pitch black and you know there isn’t much hope.

Does this sound all too familiar? If you’ve ever written more than a few lines of JavaScript, you may have experienced this darkness. There will come a time when a scary program will leave you in an empty void. At some point, it is not smart to face peril alone with primitive tools and techniques. If you are not careful, you’ll find yourself wasting hours to identify trivial bugs.

The better approach is to equip yourself with good tooling. A good debugger shortens the feedback loop and makes you more effective. The good news is Node has a very good one out of the box. The Node debugger is versatile and works with any chunk of JavaScript.

Below are strategies that have saved me from wasting valuable time in JavaScript.

The Node CLI Debugger

The Node debugger command line is a useful tool. If you are ever in a bind and can’t access a fancy editor, for any reason, this will help. The tooling uses a TCP-based protocol to debug with the debugging client. The command line client accesses the process via a port and gives you a debugging session.

You run the tool with node debug myScript.js, notice the debug flag between the two. Here are a few commands I find you must memorize:

  • sb('myScript.js', 1) set a breakpoint on first line of your script
  • c continue the paused process until you hit a breakpoint
  • repl open the debugger’s Read-Eval-Print-Loop (REPL) for evaluation

Don’t Mind the Entry Point

When you set the initial breakpoint, one tip is that it’s not necessary to set it at the entry point. Say myScript.js, for example, requires myOtherScript.js. The tool lets you set a breakpoint in myOtherScript.js although it is not the entry point.

For example:

// myScript.js
var otherScript = require('./myOtherScript');

var aDuck = otherScript();

Say that other script does:

// myOtherScript.js
module.exports = function myOtherScript() {
  var dabbler = {
    name: 'Dabbler',
    attributes: [
      { inSeaWater: false },
      { canDive: false }

  return dabbler;

If myScript.js is the entry point, don’t worry. You can still set a breakpoint like this, for example, sb('myOtherScript.js', 10). The debugger does not care that the other module is not the entry point. Ignore the warning, if you see one, as long as the breakpoint is set right. The Node debugger may complain that the module hasn’t loaded yet.

Time for a Demo of Ducks

Time for a demo! Say you want to debug the following program:

function getAllDucks() {
  var ducks = { types: [
      name: 'Dabbler',
      attributes: [
        { inSeaWater: false },
        { canDive: false }
      name: 'Eider',
      attributes: [
        { inSeaWater: true },
        { canDive: true }
    } ] };

  return ducks;


Using the CLI tooling, this is how you’d do a debugging session:

> node debug debuggingFun.js
> sb(18)
> c
> repl

Using the commands above it is possible to step through this code. Say, for example, you want to inspect the duck list using the REPL. When you put a breakpoint where it returns the list of ducks, you will notice:

> ducks
{ types:
   [ { name: 'Dabbler', attributes: [Object] },
     { name: 'Eider', attributes: [Object] } ] }

The list of attributes for each duck is missing. The reason is the REPL only gives you a shallow view when objects are deeply nested. Keep this in mind as you are spelunking through code. Consider avoiding collections that are too deep. Use variable assignments to break those out into reasonable chunks. For example, assign ducks.types[0] to a separate variable in the code. You’ll thank yourself later when pressed for time.

For example:

var dabbler = {
  name: 'Dabbler',
  attributes: [
    { inSeaWater: false },
    { canDive: false }

// ...

var ducks = { types: [
  // ...
] };
Client-Side Debugging

That’s right, the same Node tool can debug client-side JavaScript. If you conceptualize this, the Node debugger runs on top of the V8 JavaScript engine. When you feed it plain old vanilla JavaScript, the debugger will just work. There is no crazy magic here, only making effective use of the tool. The Node debugger does one job well, so take advantage of this.

Take a look at the following quick demo:

If you click on a duck, say an Eider, it will fade out. If you click it once more it will reappear. All part of fancy DOM manipulations, yes? How can you debug this code with the same server-side Node tooling?

Take a peek at the module that makes this happen:

// duckImageView.js
var DuckImageView = function DuckImageView() {

DuckImageView.prototype.onClick = function onClick(e) {
  var target = e.currentTarget;

  target.className = target.className === 'fadeOut' ? '' : 'fadeOut';

// The browser will ignore this
if (typeof module === 'object') {
  module.exports = DuckImageView;
How Is This Debuggable Through Node?

A Node program can use the code above, for example:

var assert = require('assert');
var DuckImageView = require('./duckImageView');

var event = { currentTarget: { } };

var view = new DuckImageView();

var element = event.currentTarget;

assert.equal(element.className, 'fadeOut', 'Add fadeOut class in element');

As long as your JavaScript is not tightly coupled to the DOM, you can debug it anywhere. The Node tooling doesn’t care that it is client-side JavaScript and allows this. Consider writing your modules in this way so they are debuggable. This opens up radical new ways to get yourself out of the empty void.

If you’ve ever spent time staring at an empty void, you know how painful it is to reload JavaScript in a browser. The context switch between code changes and browser reloads is brutal. With every reload, there is the opportunity to waste more time with other concerns. For example, a busted database or caching.

A better approach is to write your JavaScript so it gives you a high level of freedom. This way you can squash big nasty bugs with ease and style. The aim is you keep yourself focused on the task at hand, happy and productive. By decoupling software components, you reduce risk. Sound programming is not only about solving problems but avoiding self-inflicted issues too.

Debugging inside an Editor

Now debugging via the command line is pretty slick, but most developers don’t code in it. At least, personally, I’d prefer to spend most of my time inside a code editor. Wouldn’t it be nice if the same Node tooling could interact with the editor? The idea is to equip yourself with tooling right where you need it and that means the editor.

There are many editors out there and I can’t cover all of them here. The tool that you pick needs to make debugging accessible and easy. If you ever find yourself stuck, it’s valuable to be able to hit a shortcut key and invoke a debugger. Knowing how the computer evaluates your code as you write it is important. As for me, there is one editor that stands out as a good tool for debugging JavaScript.

Visual Studio Code is one tool I recommend for debugging JavaScript. It uses the same debugging protocol the command line tooling uses. It supports a shortcut key (F5 on both Windows and Mac), inspections, everything you expect from a good debugger.

If you already have VS Code installed and haven’t played with the debugger, do yourself a favor. Click on the debugging tab on the left and click the gear button:

A launch.json file will open up. This allows you configure the debugging entry point, for example:

  "type": "node",
  "request": "launch",
  "name": "JavaScript Tests",
  "program": "${workspaceRoot}\\entryPoint.js",
  // Point this to the same folder as the entry point
  "cwd": "${workspaceRoot}"

At a high level, you tell VS Code what to run and where. The tool supports both npm and Node entry points.

Once it is set up, set a breakpoint, hit a shortcut key and done:

The Node debugger enables you to inspect variables and step through the code. The tooling is happy to reveal what happens to the internals when it evaluates changes. All part of the necessary equipment to destroy nasty bugs.

The same principles apply across the board. Even if VS Code, for example, is not your tool of choice. You tell the tooling what to run and where. You set a breakpoint, hit a shortcut key, and get dropped into a debugging session.

Debugging Transpiled JavaScript

The same Node tooling supports transpiled JavaScript through npm packages. Each language has its own set of tools. One gotcha is each language is very different. TypeScript, for example, has different debugging tools from other transpilers. Node debugging with transpilers boils down to your framework choices and tools.

One idea is to pick the tool that integrates with your workflow. Stay close to where you are making changes and shorten the feedback loop. Give yourself the capability to set a breakpoint and hit it in less than a second.

Editors make use of source maps for debugging, so consider enabling this.

Anything short of a quick feedback loop is only asking for punishment. Your tool choices must not get in the way of sound debugging practices.


I can’t discourage enough the use of console.log() for debugging. Often I find myself in panic mode when I choose this route. It feels like shooting in the dark.

If the analogy holds true, shots fired at random can ricochet off walls and hurt you or cause friendly fire. Littering the code base with a ton of logging commands can confuse you or the next person to look at the code. I find debugging lines from a previous commit say nothing about nothing and only obfuscate the code. JavaScript can also throw exceptions if the variable does not exist, which adds to the maelstrom.

Developers at times make themselves believe they can run programs with their eyes. If one gets philosophical, the naked human eye can lie and it’s not a reliable source of truth. Your feeble sense of sight can make you believe whatever it is you want to believe and leave you in the dark.

A good debugger will give you a peek inside what the computer does with your program. This empowers you to write better software that the computer understands. The Node debugger enables you to verify changes and eliminates wishful thinking. It is a tool every good programmer should master.

Have you ever used the Node debugger? Do you have any tips or advice for debugging JavaScript? Leave comments and let me know what you think.

Top 7 Most Popular Node.js Frameworks You Should Know

Top 7 Most Popular Node.js Frameworks You Should Know

Node.js is an open-source, cross-platform, runtime environment that allows developers to run JavaScript outside of a browser. In this post, you'll see top 7 of the most popular Node frameworks at this point in time (ranked from high to low by GitHub stars).

Node.js is an open-source, cross-platform, runtime environment that allows developers to run JavaScript outside of a browser.

One of the main advantages of Node is that it enables developers to use JavaScript on both the front-end and the back-end of an application. This not only makes the source code of any app cleaner and more consistent, but it significantly speeds up app development too, as developers only need to use one language.

Node is fast, scalable, and easy to get started with. Its default package manager is npm, which means it also sports the largest ecosystem of open-source libraries. Node is used by companies such as NASA, Uber, Netflix, and Walmart.

But Node doesn't come alone. It comes with a plethora of frameworks. A Node framework can be pictured as the external scaffolding that you can build your app in. These frameworks are built on top of Node and extend the technology's functionality, mostly by making apps easier to prototype and develop, while also making them faster and more scalable.

Below are 7of the most popular Node frameworks at this point in time (ranked from high to low by GitHub stars).


With over 43,000 GitHub stars, Express is the most popular Node framework. It brands itself as a fast, unopinionated, and minimalist framework. Express acts as middleware: it helps set up and configure routes to send and receive requests between the front-end and the database of an app.

Express provides lightweight, powerful tools for HTTP servers. It's a great framework for single-page apps, websites, hybrids, or public HTTP APIs. It supports over fourteen different template engines, so developers aren't forced into any specific ORM.


Meteor is a full-stack JavaScript platform. It allows developers to build real-time web apps, i.e. apps where code changes are pushed to all browsers and devices in real-time. Additionally, servers send data over the wire, instead of HTML. The client renders the data.

The project has over 41,000 GitHub stars and is built to power large projects. Meteor is used by companies such as Mazda, Honeywell, Qualcomm, and IKEA. It has excellent documentation and a strong community behind it.


Koa is built by the same team that built Express. It uses ES6 methods that allow developers to work without callbacks. Developers also have more control over error-handling. Koa has no middleware within its core, which means that developers have more control over configuration, but which means that traditional Node middleware (e.g. req, res, next) won't work with Koa.

Koa already has over 26,000 GitHub stars. The Express developers built Koa because they wanted a lighter framework that was more expressive and more robust than Express. You can find out more about the differences between Koa and Express here.


Sails is a real-time, MVC framework for Node that's built on Express. It supports auto-generated REST APIs and comes with an easy WebSocket integration.

The project has over 20,000 stars on GitHub and is compatible with almost all databases (MySQL, MongoDB, PostgreSQL, Redis). It's also compatible with most front-end technologies (Angular, iOS, Android, React, and even Windows Phone).


Nest has over 15,000 GitHub stars. It uses progressive JavaScript and is built with TypeScript, which means it comes with strong typing. It combines elements of object-oriented programming, functional programming, and functional reactive programming.

Nest is packaged in such a way it serves as a complete development kit for writing enterprise-level apps. The framework uses Express, but is compatible with a wide range of other libraries.


LoopBack is a framework that allows developers to quickly create REST APIs. It has an easy-to-use CLI wizard and allows developers to create models either on their schema or dynamically. It also has a built-in API explorer.

LoopBack has over 12,000 GitHub stars and is used by companies such as GoDaddy, Symantec, and the Bank of America. It's compatible with many REST services and a wide variety of databases (MongoDB, Oracle, MySQL, PostgreSQL).


Similar to Express, hapi serves data by intermediating between server-side and client-side. As such, it's can serve as a substitute for Express. Hapi allows developers to focus on writing reusable app logic in a modular and prescriptive fashion.

The project has over 11,000 GitHub stars. It has built-in support for input validation, caching, authentication, and more. Hapi was originally developed to handle all of Walmart's mobile traffic during Black Friday.

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A Beginner Guide To Node.js (Basic Introduction To Node.js)

Node.js is a very popular javascript free and open source cross-platform for server-side programming built on Google Chrome’s Javascript V8 Engine. It is used by thousands of developers around the world to develop mobile and web applications. According to StackOverflow survey, Node.js is one of most famous choice for building the web application in 2018.


Node.js is a very popular javascript free and open source cross-platform for server-side programming built on Google Chrome’s Javascript V8 Engine. It is used by thousands of developers around the world to develop mobile and web applications. According to StackOverflow survey, Node.js is one of most famous choice for building the web application in 2018.

In this article, you will gain a deep understanding of node, learn how node.js works and why it is so popular among the developers and startups. Not In startup even big companies like eBay, Microsoft, GoDaddy, Paypal etc.

Why is Node.js so much popular

It is fast very fast

It’s a javascript runtime built on google chrome javascript v8 engine which means both node js and js executed in your browser running in the same engine that makes it very fast in comparison to any other server-side programming language.

It uses event-driven and non-blocking model

Node.js uses the event-driven, non-blocking I/O model that makes it very lightweight and efficient.
Now let’s understand the above statement in more details. Here I/O refers to Input /Output.

Event Driven Programming is a paradigm in which control flow of any program is determined by the occurrence of the events. All these events monitor by the code which is known as an event listener. If you are from javascript background then most probably you know what is event-listeners. In short, event-listener is a procedure or function that waits for an event to occurs. In javascript, onload, onclick, onblur most common event-listener.

**Blocking I/O **takes time and hence block other function. Consider the scenario where we want to fetch data from the database for two different users. Here we can not get the data of the second user until we did not complete the first user process. Since javascript is a single threaded and here we would have to start a new thread every time we want to fetch user data. So here Non-Blocking I/O parts come in.

Example of Blocking I/O operation

<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(‘fs’);
<span class="hljs-keyword">var</span> contents = fs.readFileSync(<span class="hljs-string">'package.json'</span>).toString();
<span class="hljs-built_in">console</span>.log(contents);

In** Non-blocking I/O **operations, you can get the user2 data without waiting for the completion of the user1 request. You can initiate both requests in parallel. **Non-blocking I/O **eliminates the need for the multi-threaded, since the system can handle multiple requests at the same time. That is the main reason which makes it very fast.

Example of Non-blocking I/O operation

<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(‘fs’);
fs.readFile(<span class="hljs-string">'package.json'</span>, <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">err, buf</span>)</span>{
    <span class="hljs-built_in">console</span>.log(buf.toString());

Note: You can learn more about the event loop and other things by going through this link.

What is Node Package Manager ( NPM )

It is is the official package manager for the node. It bundles automatically installed when you install node in your system. It is used to install new packages and manage them in useful ways. NPM install packages in two modes local and global. In the local mode, NPM installs packages in the node_module directory of the current working directory which location is owned by current user. Global packages installed in the directory where the node is installed and the location is owned by the root user.

What is the package.json

package.json is a plain JSON text file which manages all the packaged which you installed in your node application. Every Node.js applications should have this file at the root directory to describe the application metadata. A simple package.json file looks like below

    <span class="hljs-string">"name"</span> : <span class="hljs-string">"codesquery"</span>,
    <span class="hljs-string">"version"</span> : <span class="hljs-string">"1.0.0"'
    "repository": {
	"type" : "git",
	"url" : "github_repository_url"
    "dependencies": {
	"async": "0.8.0",
	"express": "4.2.x"

In the above file, name and versions are mandatory for the package.json file and rest is optional.

Installing Node.js

  • In Windows, you can install the node.js by using the installer provided by the official node.js website. Follow the installer instruction and node.js will be installed in your windows system.
  • In Linux OS, you can install the node.js by adding the PPA in your system and then install node js. Run the below command the terminal to install node js
sudo apt-get install curl python-software-properties
curl -sL https:<span class="hljs-comment">// | sudo -E bash -</span>
sudo apt-get install nodejs

  • In macOS, download the macOS installer from the official node.js website. Now run the installer by accepting the license and selecting the destination.

Test Node.js Installation

You can test the node.js installation by typing below command in the terminal

node -v

If node.js was installed successfully then you will see the installed version of the node in the terminal.

Frameworks and Tools

After gaining the popularity among the developers, there are so many frameworks built for the node js for the different type of uses. Here, I will tell you some of the most famous node js frameworks in the market

  • Express.js is the most popular framework for node.js development. A lot of popular websites is powered by express.js due to its lightweight.
  • Hapi.js is a powerful and robust framework for developing the API. This framework has features like input validation, configuration based functionality, error handling, caching and logging.
  • Metor.js is one of the most used frameworks in the node js web application development. This framework is backed by a huge community of developers, tutorials and good documentation.
  • is used to build a real-time web application like chat system and analytics. Its allow the bi-direction data flow between the web client and server.
  • Koa.js is yet another most used framework to build the web application using the node js. This framework is backed by the team behind Express.js. It allows you to ditch callbacks and increase error handling.


Today, Node.js shaping the future of web and application development technology. This is the just the basic of how node js works. If you want to build a scalable web application using the node js then you need to know more then this.

Till now, you have got the basic idea of node.js and now it is time to build something using the node.js. You can start with first by create a simple server using the node.js and then connect your node with MongoDB to perform the basic crud operation.