Debugging in NodeJS

Debugging is an essential aspect of the software development process, allowing developers to identify and resolve issues in their code efficiently.

In the context of Node.js development, debugging plays a crucial role in ensuring the reliability, performance, and functionality of applications.

In this section, we'll have an overview of the importance of debugging in the development process and explores common challenges developers face when debugging Node.js applications.

Importance of Debugging

Debugging is the process of identifying and fixing errors, bugs, and unexpected behavior in software code. It is an iterative and essential part of the development lifecycle, enabling us developers to:

• ➢Ensure Code Reliability: Debugging helps ensure that code behaves as expected under various conditions and scenarios, reducing the likelihood of runtime errors, crashes, and unexpected behavior in production environments.
• ➢Improve Code Quality: By identifying and addressing bugs early in the development process, debugging contributes to the overall quality and maintainability of the codebase, making it easier to maintain, refactor, and extend in the future.
• ➢Enhance Developer Productivity: Effective debugging tools and techniques streamline the troubleshooting process, enabling developers to diagnose and resolve issues quickly, thereby minimizing downtime and accelerating the development cycle.
• ➢Boost User Satisfaction: By delivering stable and bug-free applications, debugging contributes to a positive user experience, fostering trust and confidence in the software product.

Challenges in Debugging Node.js Applications

While debugging is essential, developers often encounter several challenges when debugging Node.js applications, including:

1. 1.Asynchrony: Node.js applications are inherently asynchronous, utilizing event-driven, non-blocking I/O operations.
   Debugging asynchronous code can be challenging, as traditional debugging techniques may not provide real-time insights into the flow of execution.
2. 2.Complexity of Stack Traces: Node.js applications often generate complex stack traces, especially in asynchronous scenarios with multiple callbacks and event handlers.
   Parsing and interpreting these stack traces to identify the root cause of errors can be daunting for developers.
3. 3.Environment Variability: Node.js applications may run in different environments, such as development, testing, staging, and production. Debugging issues that occur only in specific environments or under certain conditions requires careful configuration and testing.
4. 4.Native Add-ons and External Dependencies: Node.js applications may rely on native add-ons or external dependencies that interact with underlying C/C++ libraries or external services.
   Debugging issues related to these components requires specialized tools and techniques.
5. 5.Memory Leaks and Performance Issues: Identifying memory leaks, performance bottlenecks, and resource utilization issues in Node.js applications requires advanced profiling and monitoring tools, as well as a deep understanding of memory management and event loop mechanics.

Despite these challenges, effective debugging practices and tools can help us developers overcome obstacles and deliver high-quality, reliable Node.js applications.

In coming sections, we'll explore various debugging tools, techniques, and best practices tailored for Node.js development, empowering you to tackle debugging challenges effectively and efficiently.

Debugging Tools

Built-in Debugging Tools

Node.js provides built-in debugging tools that enable developers to inspect, analyze, and troubleshoot their applications effectively.

We'll start by exploring the Node.js Debugger (`node inspect`) and the Node.js CLI Debugger (`node --inspect-brk`).

Node.js Debugger (node inspect):

The Node.js Debugger, accessed using the node inspect command, allows developers to debug Node.js applications by attaching the debugger to a running process or starting a script in debug mode. Here's an overview of how it works:

1. 1.Attaching to a Running Process: You can attach the Node.js Debugger to a running process by specifying the process ID (PID) or target script name.
   This allows them to inspect the current state of the application, set breakpoints, and step through code execution in real-time.
   
2. 2.Debugging a Script: Alternatively, you can start a Node.js script in debug mode by running node inspect <script.js>. This launches the script in debugging mode, allowing them to set breakpoints directly within the script file and interactively debug its execution.
   

As an example, let's consider the following Node.js script (factorial.js) that defines a recursive function to calculate the factorial of a number passed in via terminal:

// factorial.js
function factorial(n) {
    if (n === 0) {
        return 1;
    } else {
        debugger
        return n * factorial(n - 1);
    }
}

const num = process.argv[2];

if (num) {
    const result = factorial(num);
    console.log(`Factorial of ${num} is:`, result);
}

To debug this snippet using the Node.js Debugger, you can run the following command in the terminal:

node inspect factorial.js 4

Upon running this command, the debugger pauses execution at the first line of the script. To instead run until the first breakpoint (specified by a debugger statement), set the NODE_INSPECT_RESUME_ON_START environment variable to 1.

NODE_INSPECT_RESUME_ON_START=1 node inspect play.js 4

We can set a breakpoint inside the factorial function to inspect the recursive calls and their results.

Breakdown:

• ➢The debugger should pause execution at the debugger statement in the snippet.
• ➢you can step through each recursive call of the factorial function by entering `c` or `cont`
• ➢After reaching the base case (if (n === 0)), the debugger should return the result (1) and unwind the call stack to calculate the factorial of the given number, which in this case is 4.
• ➢You inspect the value of n in each iteration by entering repl command which allows code to be evaluated remotely. In our case that will look like:

< Debugger listening on ws://127.0.0.1:9229/a1e63a67-2951-4934-8ba1-c89fc97d1e8c
< For help, see: https://nodejs.org/en/docs/inspector
< 
< Debugger attached.
< 
 ok
break in play.js:6
  4         return 1;
  5     } else {
> 6         debugger
  7         return n * factorial(n - 1);
  8     }
debug> c
break in play.js:6
  4         return 1;
  5     } else {
> 6         debugger
  7         return n * factorial(n - 1);
  8     }
debug> repl
Press Ctrl+C to leave debug repl
> n
3

Stepping command:

• ➢cont, c: Continue execution
• ➢next, n: Step next
• ➢step, s: Step in
• ➢out, o: Step out
• ➢pause: Pause running code (like pause button in Developer Tools)

Node.js CLI Debugger (node --inspect-brk):

The Node.js CLI Debugger, accessed using the node --inspect-brk command, enables developers to debug Node.js applications using the Chrome DevTools Protocol. Here's how it works:

1. 1.Starting in Break Mode: When running a Node.js script with the --inspect-brk flag, the debugger pauses execution at the first line of the script, allowing you to set breakpoints before the script begins executing.
   
2. 2.Debugging with Chrome DevTools: You can then connect to the debugging session using Chrome DevTools or another compatible debugger, enabling them to inspect the application state, set breakpoints, and step through code execution in a familiar browser-based interface
   

As an example, consider the same Node.js script (factorial.js) from the previous example.

To debug it using the Node.js CLI Debugger, we can run the following command in the terminal:

NODE_INSPECT_RESUME_ON_START=1 node --inspect-brk play.js 4

This command starts the script in debug mode and pauses execution at the debugger statement in the script.

You can then open Chrome DevTools and navigate to chrome://inspect to connect to the debugging session and debug the script interactively.

when you navigate to chrome://inspect you should have something similar to image below:

After clicking on the inpsect line, a new chrome inspect window will be launched.

Within the chrome DevTools interface, there's more flexibility in debugging your code. Also the view is very well structured and organize to ease code behavior inspection.

Although these tools provide powerful capabilities for debugging Node.js applications, allowing developers to inspect, analyze, and troubleshoot code effectively, there are more advanced debugging techniques and third-party debugging tools for Node.js development.

Debugging with Visual Studio Code

Visual Studio Code (VS Code) is a popular integrated development environment (IDE) that provides powerful built-in debugging features for Node.js applications.

We'll be setting up launch configurations, using breakpoints, inspecting variables, and stepping through code execution within VS code.

Setting up Launch Configurations

Launch configurations in VS Code define how a Node.js application should be executed and debugged. To set up a launch configuration for a Node.js application, follow these steps:

1. 1.Open your project in VS Code.
2. 2.Click on the Debug icon in the Activity Bar on the side panel.
3. 3.Click on the gear icon (⚙️) to open the `launch.json` file.
4. 4.Add a new configuration or modify an existing one to specify the entry point of your Node.js application and any additional arguments or environment variables.
5. 5.Save the launch.json file.

Here is sample config object you can copy and adapt to you environment and project.

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [

        {
            "type": "node",
            "request": "launch",
            "name": "Launch Program",
            "runtimeExecutable": "/Users/donaldteghen/.nvm/versions/node/v20.11.1/bin/node",
            "skipFiles": [
                "<node_internals>/**"
            ],
            "program": "${workspaceFolder}/app.js",
          "runtimeArgs": [
            "--inspect-brk"
          ],
          "port": 9001
        }
    ]
}

This launch configuration specifies the entry point of the Node.js application (app.js), enables debugging with the --inspect-brk flag to pause execution at the first line, and sets the debugger port to 9001.

Using Breakpoints and Inspecting Variables

Breakpoints allow developers to pause execution at specific lines of code and inspect the application state.

To set a breakpoint in VS Code, click on the gutter next to the line of code where you want to pause execution.

You can then inspect variables, evaluate expressions, and step through code execution using the debug toolbar or keyboard shortcuts(Just as we saw with chrome devtools UI).

Here is our app.js content:

// app.js

let iterations = 0;
function subtractByFiveIteratively(n) { 
    if (n <= 0) {          // set breakpoint here
        return iterations  // set breakpoint here
    }
    iterations++;           // set breakpoint here
    return subtractByFiveIteratively(n - 5);
}
console.log(`Number of 5s in 78 is:`, subtractByFiveIteratively(78));

Once you're set, run the debugger and you should have something similar to the image below:

In this example, we set a breakpoint on three lines. When we run the application in debug mode, execution will pause at these lines on each iteration, allowing us to inspect the values of n, and iterations.

Stepping Through Code Execution

VS Code provides several options for stepping through code execution:

• ➢Step Over (F10): Executes the current line of code and moves to the next line in the current function.
• ➢Step Into (F11): If the current line of code calls a function, steps into the function and pauses at the first line of the function body.
• ➢Step Out (Shift + F11): If the debugger is paused inside a function, executes the remaining lines of the function and pauses at the line following the function call.

By using these stepping commands, developers can navigate through the codebase, understand the flow of execution, and identify potential issues more effectively.

Conclusion

To conclude, debugging is an integral parts of the software development process, enabling developers to ensure the quality, reliability, and performance of their Node.js applications.

By adopting best practices, leveraging appropriate tools and techniques, and fostering a culture of continuous improvement, you can streamline your debugging workflows, identify and resolve issues efficiently, and deliver robust and reliable Node.js applications to end users.

This marks the end of this theorically introductory tutorial series on Node.js. Most of the concepts convered had illustrative, yet, isolated examples and usecases.

In the final chapter of this series, we will design and build a complete Node.js app with features derived from the concepts discussed throughout this series.