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;
}

getAllDucks();

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: [
  dabbler,
  // ...
] };
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();
view.onClick(event);

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.

Conclusion

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).

Express

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

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

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

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

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

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).

Hapi

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.

Node.js for Beginners - Learn Node.js from Scratch (Step by Step)

Node.js for Beginners - Learn Node.js from Scratch (Step by Step)

Node.js for Beginners - Learn Node.js from Scratch (Step by Step) - Learn the basics of Node.js. This Node.js tutorial will guide you step by step so that you will learn basics and theory of every part. Learn to use Node.js like a professional. You’ll learn: Basic Of Node, Modules, NPM In Node, Event, Email, Uploading File, Advance Of Node.

Node.js for Beginners

Learn Node.js from Scratch (Step by Step)

Welcome to my course "Node.js for Beginners - Learn Node.js from Scratch". This course will guide you step by step so that you will learn basics and theory of every part. This course contain hands on example so that you can understand coding in Node.js better. If you have no previous knowledge or experience in Node.js, you will like that the course begins with Node.js basics. otherwise if you have few experience in programming in Node.js, this course can help you learn some new information . This course contain hands on practical examples without neglecting theory and basics. Learn to use Node.js like a professional. This comprehensive course will allow to work on the real world as an expert!
What you’ll learn:

  • Basic Of Node
  • Modules
  • NPM In Node
  • Event
  • Email
  • Uploading File
  • Advance Of Node

How to Use Express.js, Node.js and MongoDB.js

How to Use Express.js, Node.js and MongoDB.js

In this post, I will show you how to use Express.js, Node.js and MongoDB.js. We will be creating a very simple Node application, that will allow users to input data that they want to store in a MongoDB database. It will also show all items that have been entered into the database.

In this post, I will show you how to use Express.js, Node.js and MongoDB.js. We will be creating a very simple Node application, that will allow users to input data that they want to store in a MongoDB database. It will also show all items that have been entered into the database.

Creating a Node Application

To get started I would recommend creating a new database that will contain our application. For this demo I am creating a directory called node-demo. After creating the directory you will need to change into that directory.

mkdir node-demo
cd node-demo

Once we are in the directory we will need to create an application and we can do this by running the command
npm init

This will ask you a series of questions. Here are the answers I gave to the prompts.

The first step is to create a file that will contain our code for our Node.js server.

touch app.js

In our app.js we are going to add the following code to build a very simple Node.js Application.

var express = require("express");
var app = express();
var port = 3000;
 
app.get("/", (req, res) => {
  res.send("Hello World");
});
 
app.listen(port, () => {
  console.log("Server listening on port " + port);
});

What the code does is require the express.js application. It then creates app by calling express. We define our port to be 3000.

The app.use line will listen to requests from the browser and will return the text “Hello World” back to the browser.

The last line actually starts the server and tells it to listen on port 3000.

Installing Express

Our app.js required the Express.js module. We need to install express in order for this to work properly. Go to your terminal and enter this command.

npm install express --save

This command will install the express module into our package.json. The module is installed as a dependency in our package.json as shown below.

To test our application you can go to the terminal and enter the command

node app.js

Open up a browser and navigate to the url http://localhost:3000

You will see the following in your browser

Creating Website to Save Data to MongoDB Database

Instead of showing the text “Hello World” when people view your application, what we want to do is to show a place for user to save data to the database.

We are going to allow users to enter a first name and a last name that we will be saving in the database.

To do this we will need to create a basic HTML file. In your terminal enter the following command to create an index.html file.

touch index.html

In our index.html file we will be creating an input filed where users can input data that they want to have stored in the database. We will also need a button for users to click on that will add the data to the database.

Here is what our index.html file looks like.

<!DOCTYPE html>
<html>
  <head>
    <title>Intro to Node and MongoDB<title>
  <head>

  <body>
    <h1>Into to Node and MongoDB<&#47;h1>
    <form method="post" action="/addname">
      <label>Enter Your Name<&#47;label><br>
      <input type="text" name="firstName" placeholder="Enter first name..." required>
      <input type="text" name="lastName" placeholder="Enter last name..." required>
      <input type="submit" value="Add Name">
    </form>
  <body>
<html>

If you are familiar with HTML, you will not find anything unusual in our code for our index.html file. We are creating a form where users can input their first name and last name and then click an “Add Name” button.

The form will do a post call to the /addname endpoint. We will be talking about endpoints and post later in this tutorial.

Displaying our Website to Users

We were previously displaying the text “Hello World” to users when they visited our website. Now we want to display our html file that we created. To do this we will need to change the app.use line our our app.js file.

We will be using the sendFile command to show the index.html file. We will need to tell the server exactly where to find the index.html file. We can do that by using a node global call __dirname. The __dirname will provide the current directly where the command was run. We will then append the path to our index.html file.

The app.use lines will need to be changed to
app.use("/", (req, res) => {   res.sendFile(__dirname + "/index.html"); });

Once you have saved your app.js file, we can test it by going to terminal and running node app.js

Open your browser and navigate to “http://localhost:3000”. You will see the following

Connecting to the Database

Now we need to add our database to the application. We will be connecting to a MongoDB database. I am assuming that you already have MongoDB installed and running on your computer.

To connect to the MongoDB database we are going to use a module called Mongoose. We will need to install mongoose module just like we did with express. Go to your terminal and enter the following command.
npm install mongoose --save

This will install the mongoose model and add it as a dependency in our package.json.

Connecting to the Database

Now that we have the mongoose module installed, we need to connect to the database in our app.js file. MongoDB, by default, runs on port 27017. You connect to the database by telling it the location of the database and the name of the database.

In our app.js file after the line for the port and before the app.use line, enter the following two lines to get access to mongoose and to connect to the database. For the database, I am going to use “node-demo”.

var mongoose = require("mongoose"); mongoose.Promise = global.Promise; mongoose.connect("mongodb://localhost:27017/node-demo");

Creating a Database Schema

Once the user enters data in the input field and clicks the add button, we want the contents of the input field to be stored in the database. In order to know the format of the data in the database, we need to have a Schema.

For this tutorial, we will need a very simple Schema that has only two fields. I am going to call the field firstName and lastName. The data stored in both fields will be a String.

After connecting to the database in our app.js we need to define our Schema. Here are the lines you need to add to the app.js.
var nameSchema = new mongoose.Schema({   firstName: String,   lastNameName: String });

Once we have built our Schema, we need to create a model from it. I am going to call my model “DataInput”. Here is the line you will add next to create our mode.
var User = mongoose.model("User", nameSchema);

Creating RESTful API

Now that we have a connection to our database, we need to create the mechanism by which data will be added to the database. This is done through our REST API. We will need to create an endpoint that will be used to send data to our server. Once the server receives this data then it will store the data in the database.

An endpoint is a route that our server will be listening to to get data from the browser. We already have one route that we have created already in the application and that is the route that is listening at the endpoint “/” which is the homepage of our application.

HTTP Verbs in a REST API

The communication between the client(the browser) and the server is done through an HTTP verb. The most common HTTP verbs are
GET, PUT, POST, and DELETE.

The following table explains what each HTTP verb does.

HTTP Verb Operation
GET Read
POST Create
PUT Update
DELETE Delete

As you can see from these verbs, they form the basis of CRUD operations that I talked about previously.

Building a CRUD endpoint

If you remember, the form in our index.html file used a post method to call this endpoint. We will now create this endpoint.

In our previous endpoint we used a “GET” http verb to display the index.html file. We are going to do something very similar but instead of using “GET”, we are going to use “POST”. To get started this is what the framework of our endpoint will look like.

app.post("/addname", (req, res) => {
 
});
Express Middleware

To fill out the contents of our endpoint, we want to store the firstName and lastName entered by the user into the database. The values for firstName and lastName are in the body of the request that we send to the server. We want to capture that data, convert it to JSON and store it into the database.

Express.js version 4 removed all middleware. To parse the data in the body we will need to add middleware into our application to provide this functionality. We will be using the body-parser module. We need to install it, so in your terminal window enter the following command.

npm install body-parser --save

Once it is installed, we will need to require this module and configure it. The configuration will allow us to pass the data for firstName and lastName in the body to the server. It can also convert that data into JSON format. This will be handy because we can take this formatted data and save it directly into our database.

To add the body-parser middleware to our application and configure it, we can add the following lines directly after the line that sets our port.

var bodyParser = require('body-parser');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
Saving data to database

Mongoose provides a save function that will take a JSON object and store it in the database. Our body-parser middleware, will convert the user’s input into the JSON format for us.

To save the data into the database, we need to create a new instance of our model that we created early. We will pass into this instance the user’s input. Once we have it then we just need to enter the command “save”.

Mongoose will return a promise on a save to the database. A promise is what is returned when the save to the database completes. This save will either finish successfully or it will fail. A promise provides two methods that will handle both of these scenarios.

If this save to the database was successful it will return to the .then segment of the promise. In this case we want to send text back the user to let them know the data was saved to the database.

If it fails it will return to the .catch segment of the promise. In this case, we want to send text back to the user telling them the data was not saved to the database. It is best practice to also change the statusCode that is returned from the default 200 to a 400. A 400 statusCode signifies that the operation failed.

Now putting all of this together here is what our final endpoint will look like.

app.post("/addname", (req, res) => {
  var myData = new User(req.body);
  myData.save()
    .then(item => {
      res.send("item saved to database");
    })
    .catch(err => {
      res.status(400).send("unable to save to database");
    });
});
Testing our code

Save your code. Go to your terminal and enter the command node app.js to start our server. Open up your browser and navigate to the URL “http://localhost:3000”. You will see our index.html file displayed to you.

Make sure you have mongo running.

Enter your first name and last name in the input fields and then click the “Add Name” button. You should get back text that says the name has been saved to the database like below.

Access to Code

The final version of the code is available in my Github repo. To access the code click here. Thank you for reading !