debug

Environment Variable Configuration

Environment Variable Configuration

Imagine you have a secret recipe for your favorite dish, and you've written it down on a piece of paper. You don't want to share the recipe with everyone, so you keep it locked away in a special box.

In Node.js debugging, environment variables are like that special box. They hold sensitive information that you don't want to be publicly accessible.

Setting Environment Variables

Just like you put the recipe in the box, you can set environment variables using the process.env object. The syntax is like this:

process.env.MY_SECRET = 'my_secret_value';

Accessing Environment Variables

To use the secret recipe, you need to get it out of the box. Similarly, you can access environment variables using the same process.env object:

const mySecret = process.env.MY_SECRET; // 'my_secret_value'

Real-World Applications

Environment variables are useful for storing sensitive information like API keys, database passwords, or other secrets. They can be used in any Node.js application, but they are especially useful in cloud environments like Heroku or AWS, where you need to keep your secrets secure.

Complete Code Example

// Set an environment variable
process.env.API_KEY = 'my_api_key';

// Access an environment variable
const apiKey = process.env.API_KEY; // 'my_api_key'

Potential Applications

  • Storing database passwords

  • API keys for external services

  • Encryption keys for data security

  • Configuration options for different environments (e.g., development, production)

Integration with Other Logging Libraries

What is Integration with Other Logging Libraries?

Integration with other logging libraries means that you can use functions from one logging library inside another logging library.

Integrating with Winston

Winston is a popular logging library that provides a convenient way to log messages using different transports.

Example

const debug = require('debug')('my-app');
const winston = require('winston');

// Create a Winston logger
const logger = winston.createLogger({
  format: winston.format.simple(),
  transports: [new winston.transports.Console()],
});

// Add a debug function to the Logger
logger.debug = debug;

// Log a message using the debug function
logger.debug('This is a debug message');

Integrating with Pino

Pino is a fast and lightweight logging library that provides a structured logging API.

Example

const debug = require('debug');
const pino = require('pino');

// Create a Pino logger
const logger = pino();

// Add a debug function to the Logger
logger.debug = debug('my-app');

// Log a message using the debug function
logger.debug('This is a debug message');

Real-World Applications

These integrations allow you to use the features of both logging libraries in the same application.

For example, you could useWinston for its support for different transports and Pino for its structured logging API.

Or you could use debug to add detailed logging to a Pino logger, providing more information about the application's execution.

Contributing to Debug

Contributing to debug

1. Install the dependencies.

npm install

2. Run the tests.

npm test

3. Make your changes.

4. Run the tests again.

npm test

5. Push your changes to GitHub.

git push origin main

6. Create a pull request.

Visit the debug GitHub repository and click the "New pull request" button.

7. Fill out the pull request template.

The pull request template will ask you to provide a description of your changes, as well as any relevant tests or documentation.

8. Submit the pull request.

Once you have filled out the pull request template, click the "Submit pull request" button.

9. Wait for the pull request to be reviewed.

A debug maintainer will review your pull request and either merge it or request changes.

10. Merge the pull request.

Once the pull request has been approved, a debug maintainer will merge it into the main branch.

Code of Conduct

Please be respectful of other contributors. The debug project is a welcoming place for all, regardless of gender, race, religion, sexual orientation, or disability.

Code Style

The debug project uses the following code style:

  • 2 spaces for indentation

  • No semicolons

  • Single quotes

  • No trailing commas

Pull Request Checklist

Before submitting a pull request, please make sure that you have:

  • Run the tests

  • Followed the code style

  • Filled out the pull request template

Potential Applications

The debug module can be used in a variety of applications, including:

  • Debugging web applications

  • Debugging Node.js applications

  • Debugging mobile applications

  • Debugging embedded systems

Best Practices

Best Practices for Node.js Debugging

1. Use a Debugger

Imagine a debugger as a special "microscope" for your code. It helps you peek inside your program and inspect its variables, execution flow, and more. Some popular debuggers for Node.js include:

  • Node.js debugger (built-in)

  • VSCode debugger (integrated into Visual Studio Code)

  • Chrome DevTools

2. Set Breakpoints

Breakpoints are like little markers you place in your code to tell the debugger to pause when it reaches that point. This allows you to examine the state of your program at a specific moment.

// Set a breakpoint at line 10
debugger;

3. Examine Variables

Once you've paused your program, you can use the debugger to inspect the values of variables. Think of it as reading the memory of your computer, but in a much more convenient way.

// Inspect the value of the 'x' variable
console.log(x);

4. Step Through Code

Stepping through code allows you to follow the execution of your program line by line. It's like stepping into the code and experiencing it yourself.

  • Step over: Advance to the next line without entering functions.

  • Step into: Enter a function and execute its code.

  • Step out: Exit a function and resume execution in the calling code.

5. Evaluate Expressions

Sometimes, you need to check the result of an expression without modifying your code. The debugger allows you to evaluate expressions on the fly.

// Evaluate the expression 'Math.pow(2, 10)'
console.log(Math.pow(2, 10));

6. Log Messages

Logging messages is a great way to track the progress of your program and see what's happening behind the scenes. You can add console.log() statements to output messages at specific points during execution.

// Log a message when the user clicks the button
button.addEventListener('click', () => {
  console.log('Button clicked!');
});

Potential Applications in Real World:

  • Finding bugs and errors in your code

  • Understanding the flow of your program

  • Investigating performance issues

  • Analyzing the behavior of external libraries and APIs

Disabling Debug Output

Disabling Debug Output

Sometimes you need to hide debug messages. There are two ways to do so:

1. Environment Variable:

You can set the DEBUG environment variable to "" (empty string) to turn off all debug output.

# Disable debug output
DEBUG=""

# Run your script
node my-script.js

2. Programmatically:

You can use the debug module to disable debug output programmatically.

const debug = require('debug');

// Disable debug output for all namespaces
debug.disable();

// Run your code without debug messages

Real-World Applications:

  • Test environments: Disable debug output to reduce noise in test results.

  • Production deployments: Prevent debug messages from leaking sensitive information to users.

  • Performance improvements: Disabling verbose debug messages can improve performance by reducing unnecessary processing.

Error Handling and Debugging

Error Handling and Debugging

1. Error Types

  • Syntax Errors: Errors that prevent the code from running, such as missing parentheses or semicolons.

  • Runtime Errors: Errors that occur while the code is running, such as attempting to access a variable that doesn't exist.

  • Logical Errors: Errors that cause the code to produce incorrect results, such as dividing by zero.

2. Error Handling

  • try/catch: A block of code that tries to execute a set of statements. If an error occurs, the catch block is executed.

  • throw: Used to throw an error explicitly.

  • Error Handling Middleware: ExpressJS middleware, such as errorHandler, can catch and handle errors in web applications.

Example:

// try/catch
try {
  console.log(undefinedVariable); // Runtime Error
} catch (error) {
  console.log('Error:', error.message);
}

// throw
function divide(numerator, denominator) {
  if (denominator === 0) {
    throw new Error('Cannot divide by zero'); // Logical Error
  }
  return numerator / denominator;
}

3. Debugging

  • Node.js Debugger: A built-in tool that allows you to step through code, inspect variables, and set breakpoints.

  • debugger: The keyword used to pause execution and enter the debugger.

  • Console Logging: Using console.log() to print messages and track code execution.

Example:

debugger; // Pauses execution
console.log(variable); // Prints variable value

4. Potential Applications

  • Error Reporting: Capturing and reporting errors to a central location for analysis and troubleshooting.

  • Code Validation: Ensuring that code is syntactically and logically correct before deploying it.

  • Debugging Complex Applications: Quickly identifying and fixing issues in large and complex codebases.

Using Debug in Development vs. Production

Using Debug in Development vs. Production

Debug is a Node.js package that helps you troubleshoot your code. It works by setting breakpoints and logging messages to the console.

Development

In development, you want to be able to debug your code easily. This means setting breakpoints and logging messages to the console. Debug is a great tool for this because it provides a user-friendly interface for setting breakpoints and inspecting variables.

To use Debug in development, you first need to install it as a dependency:

npm install --save-dev debug

Then, you can require Debug and use it to set breakpoints:

const debug = require('debug')('my-app');

debug('This is a debug message');

You can also use Debug to log messages to the console:

debug('This is a debug message');

Production

In production, you don't want to have any debugging code in your codebase. This is because debugging code can add overhead to your application and make it less secure.

To disable debugging code in production, you can set the NODE_DEBUG environment variable to an empty string:

NODE_DEBUG="" node my-app.js

You can also use the Debug package to disable debugging code in production by passing the production option to the debug() function:

const debug = require('debug')('my-app', { production: true });

debug('This is a debug message');

Real-World Examples

Here are some real-world examples of how you can use Debug:

  • Troubleshooting a Node.js application: You can use Debug to set breakpoints and log messages to the console to help you troubleshoot a Node.js application. This can be helpful if you're having trouble understanding why your application is behaving the way it is.

  • Debugging a Node.js module: You can use Debug to set breakpoints and log messages to the console to help you debug a Node.js module. This can be helpful if you're having trouble understanding how the module works or if you're trying to fix a bug.

  • Inspecting the state of a Node.js application: You can use Debug to inspect the state of a Node.js application at any point in time. This can be helpful if you're trying to understand how your application is behaving or if you're trying to diagnose a problem.

Potential Applications

Debug can be used in a variety of different applications, including:

  • Web development: You can use Debug to help you troubleshoot your web applications. This can be helpful if you're having trouble understanding why your application is behaving the way it is or if you're trying to fix a bug.

  • Mobile development: You can use Debug to help you troubleshoot your mobile applications. This can be helpful if you're having trouble understanding why your application is behaving the way it is or if you're trying to fix a bug.

  • Desktop development: You can use Debug to help you troubleshoot your desktop applications. This can be helpful if you're having trouble understanding why your application is behaving the way it is or if you're trying to fix a bug.

Debug Release Notes

Debugger Updates

Easier Debugging with Aliased Breakpoints

Simplified: Imagine breakpoints as special bookmarks in your code. Now, you can give them custom names, making it easier to find and manage them.

Example:

// Create an aliased breakpoint named "my-custom-breakpoint" at line 10
debugger; // { alias: "my-custom-breakpoint" }

Benefits:

  • Helps organize and identify breakpoints in complex codebases.

  • Reduces confusion during debugging sessions.

Remote Debugging for Docker

Simplified: Allows you to debug containerized applications running inside Docker environments from your local machine.

Example:

docker-compose exec <container-name> node --inspect-brk 8080 your-script.js

Benefits:

  • Enables efficient debugging of Docker-based applications.

  • Simplifies troubleshooting issues within containers.

Heap Profiling

Simplified: Tracks memory usage of your application and helps identify potential memory leaks or bottlenecks.

Example:

const { HeapProfiler } = require('v8');

const profiler = new HeapProfiler();
profiler.startTrackingHeapObjects();

// Execute code that may allocate a lot of memory

profiler.stopTrackingHeapObjects();
const snapshot = profiler.takeHeapSnapshot();

Benefits:

  • Detects memory issues early on, reducing the risk of performance problems.

  • Helps optimize memory usage and minimize resource consumption.

Real-World Applications

  • Aliased Breakpoints: Used in large codebases to organize breakpoints for specific scenarios or debugging purposes.

  • Docker Debugging: Enables debugging of microservices or distributed systems running within Docker containers.

  • Heap Profiling: Essential for performance analysis and optimization, especially in memory-intensive applications.

Custom Formatters

Custom Formatters

Custom formatters are used to customize the output of the debugger. By default, the debugger uses the built-in repl formatter, which displays the values of variables and expressions in a REPL (read-eval-print loop) format.

Creating a Custom Formatter:

To create a custom formatter, you can implement the debug.Formatters interface. This interface has three methods:

  1. name: Returns the name of the formatter.

  2. init: Initializes the formatter.

  3. format: Formats the value of a variable or expression.

Example:

Here's an example of a custom formatter that formats objects as JSON:

const { Formatters } = require('debug');

const jsonFormatter = new Formatters.ObjectFormatter();

jsonFormatter.format = function(obj) {
  return JSON.stringify(obj, null, 2);
};

debug('myapp', jsonFormatter);

Now, when you use debug('myapp') to log objects, they will be displayed as JSON.

Potential Applications:

Custom formatters can be used to:

  • Display values in a different format (e.g., JSON, XML, etc.)

  • Add additional information to the output (e.g., timestamps, call stack, etc.)

  • Integrate with other debugging tools (e.g., Visual Studio Code, WebStorm, etc.)

Complete Code Implementation:

Here's a complete code implementation of the JSON formatter example:

const { Formatters, transports } = require('debug');

// Create a JSON formatter
const jsonFormatter = new Formatters.ObjectFormatter();

// Customize the format method to return JSON
jsonFormatter.format = function(obj) {
  return JSON.stringify(obj, null, 2);
};

// Create a debug instance with the JSON formatter
const debug = debug('myapp', jsonFormatter);

// Log an object
debug({ foo: 'bar', baz: [1, 2, 3] });

This will output the following JSON to the console:

{
  "foo": "bar",
  "baz": [
    1,
    2,
    3
  ]
}

Namespaces

Namespaces

In Node.js, namespaces provide a way to organize and group related code and data within a single module. They allow you to define a scope for identifiers, such as variables, functions, and classes, within a module. This is useful for avoiding naming conflicts and enhancing code readability and organization.

Creating Namespaces

To create a namespace, you can use the namespace keyword followed by the name of the namespace, enclosed in curly braces. Within the namespace, you can define variables, functions, and classes.

namespace MyNamespace {
  let name = "John";
  function sayHello() {
    console.log("Hello from MyNamespace!");
  }
}

Accessing Namespace Members

To access members of a namespace, you need to prefix the member name with the namespace name, separated by a period (.).

MyNamespace.name; // "John"
MyNamespace.sayHello(); // Prints "Hello from MyNamespace!"

Real-World Applications

Namespaces are frequently used in Node.js applications to organize code into logical groups:

  • Modularizing Code: Namespaces allow you to break down complex code into smaller, manageable modules.

  • Avoiding Name Conflicts: By using namespaces, you can ensure that identifiers used within a module do not conflict with those used in other modules.

  • Enhancing Code Readability: Namespaces make it easier to navigate and understand the structure of a codebase by providing clear groupings of related code.

Complete Code Implementation

Here is an example of a complete code implementation that uses namespaces:

// user.js
namespace UserModule {
  class User {
    constructor(name, age) {
      this.name = name;
      this.age = age;
    }

    greet() {
      console.log(`Hello, my name is ${this.name}.`);
    }
  }
}

// main.js
import { UserModule } from "./user";

const user = new UserModule.User("John", 30);
user.greet(); // Prints "Hello, my name is John."

Basic Usage

Basic Usage

Debugging Your Node.js Code

1. Enable Debugging Mode

  • Add "debugger;" statement in your code where you want the debugger to pause.

  • Run your program with node --inspect.

Example:

// Set a breakpoint in the following line
debugger;

console.log("Hello, world!");

When you run this program with node --inspect, the debugger will pause at the debugger; statement.

2. Open the Debugger

  • Open your browser and go to chrome://inspect/#devices.

  • Click on the "inspect" link for your Node.js process.

3. Debug Your Code

  • Use the debugger's interface to inspect variables, set breakpoints, and step through your code.

  • The "Sources" tab shows your code files and allows you to set breakpoints.

  • The "Variables" tab shows the current values of variables at the current breakpoint.

Example:

  • Open the "Variables" tab to see the value of x at the debugger; statement.

  • Click the "Step Over" button to execute the next line of code.

4. Potential Applications

  • Finding and fixing bugs in complex code.

  • Inspecting the state of your program at specific points.

  • Debugging multi-threaded or asynchronous code.

Custom Logging Functions

Custom Logging Functions

What are Custom Logging Functions?

Custom logging functions allow you to add custom logic to your logging system. They let you do things like format your logs in a specific way, filter out unwanted logs, or send logs to a different destination.

How to Use Custom Logging Functions:

  1. Create a function: Define a function that takes the log entry as an argument and returns a new log entry or undefined.

  2. Register the function: Use the functions.logger function to register your function with your logger.

Example:

// Create a function to format logs to JSON
const formatJSON = entry => {
  return {
    message: entry.message,
    level: entry.level,
    timestamp: entry.timestamp,
  };
};

// Register the function
logger.functions.register(formatJSON);

Now, all logs will be formatted as JSON.

Real World Applications:

  • Filter logs: Filter out any logs that don't match a certain criteria.

  • Transform logs: Convert logs to a different format, such as JSON or XML.

  • Send logs to a different destination: Send logs to a specific database, file, or cloud service.

  • Anonymize logs: Remove sensitive data from logs before they get sent to a 3rd party.

Complete Code Implementation:

// Import the logger
const {logger} = require('debug');

// Create a function to filter out logs that don't contain "error"
const filterErrors = entry => {
  return entry.message.includes('error') ? entry : undefined;
};

// Register the function
logger.functions.register(filterErrors);

// Log an error
logger.error('Error occurred!');

// Will not be logged because it doesn't contain "error"
logger.info('Info message');

Output:

{
  "message": "Error occurred!",
  "level": "error",
  "timestamp": "2023-03-08T16:37:31.949Z"
}

Potential Applications:

  • Compliance: Filter out logs that don't meet compliance regulations.

  • Security: Anonymize logs before sending them to a 3rd party.

  • Data Analysis: Transform logs to a format that's easier to analyze.

  • Error Handling: Send error logs to a specific email address or notification service.

Browser Support

Browser Support

Node.js Debugger supports remote debugging in web browsers. This allows you to inspect and control JavaScript code running in the browser from your text editor.

Requirements

  • A modern web browser (Chrome, Firefox, Edge, or Safari)

  • The Node.js Debugger extension installed in your browser

  • A Node.js application running in the browser

Setup

  1. Install the Node.js Debugger extension in your browser.

  2. Start your Node.js application in the browser.

  3. Open the debugger in your text editor (e.g., Visual Studio Code, WebStorm) and click the "Attach to Browser" button.

Debugging

Once the debugger is attached to the browser, you can inspect the JavaScript code running in the browser. This includes:

  • Setting breakpoints

  • Stepping through code

  • Inspecting variables

  • Evaluating expressions

  • Profiling code

Applications

Browser support for the Node.js Debugger allows you to:

  • Quickly debug JavaScript code running in the browser

  • Improve the performance of your web applications

  • Enhance the user experience of your web applications

Example

Here is an example of how to debug a Node.js application running in the browser using Visual Studio Code:

  1. Open your Node.js project in Visual Studio Code.

  2. Install the Node.js Debugger extension.

  3. Start your Node.js application in the browser.

  4. Open the debugger in Visual Studio Code and click the "Attach to Browser" button.

  5. Set a breakpoint in the JavaScript code running in the browser.

  6. Reload the web page in the browser to trigger the breakpoint.

  7. Step through the code, inspect variables, and evaluate expressions to debug the issue.

Installation and Setup

Simplified Installation and Setup for Node.js Debugger

1. Installation

  • Install the Node.js debugger package: npm install --save-dev nodemon

2. Setup

  • Add a script to your package.json file:

{
  "scripts": {
    "debug": "nodemon"
  }
}

3. Usage

  • Run the debugger script: npm run debug

Explanation:

1. Installation:

  • nodemon installs the debugger as a "development dependency" for your Node.js project. This means it's only installed locally, not in your production environment.

2. Setup:

  • The script in package.json tells the debugger how to run your Node.js application. The command nodemon automatically restarts your app when you make changes, making debugging easier.

3. Usage:

  • Running npm run debug starts the debugger and runs your application. When you make changes to your code, the debugger will automatically restart the app, showing any errors or debugging information you need.

Real-World Examples:

  • Troubleshooting Errors: Use the debugger to trace errors and identify the source of issues in your code.

  • Testing and Debugging: Set breakpoints and inspect variables to verify the behavior of your application and detect any bugs.

  • Code Optimization: Use the debugger to analyze code performance and identify areas for improvement.

  • Development Environment: The debugger helps developers create and debug Node.js applications with ease and speed.

Using Debug in Other Modules

Debugging Other Modules

In Node.js, you can use the debug package to debug not only your own code but also third-party modules.

Setting Up

To enable debugging in other modules, you first need to install debug:

npm install debug

Using debug in Other Modules

  1. Import debug: Import the debug package into the module you want to debug.

const debug = require('debug');

  1. Create a Debugger: Create a debugger instance with a namespace. The namespace is used to group related debug messages.

const myDebug = debug('my-module-name:my-function');

  1. Log Debug Messages: Use the debug function to log debug messages. If the debug namespace is enabled, the message will be printed to the console.

myDebug('This is a debug message'); // Logs only if 'my-module-name:my-function' is enabled

Enabling Debugging

To enable debugging for a particular namespace, set the DEBUG environment variable:

DEBUG=my-module-name:my-function node index.js

Example

Here's a complete example of debugging a third-party module:

// Helper module
const debug = require('debug');
const myDebug = debug('helper-module');

module.exports = {
  doSomething: () => {
    myDebug('Doing something...');
  }
}

// Main module
const helper = require('./helper-module');

// Enable debugging for 'helper-module'
process.env.DEBUG = 'helper-module';

// Call the function from helper module
helper.doSomething(); // Logs 'Doing something...' to the console

Real-World Applications

  • Debugging issues in external dependencies or libraries

  • Identifying performance bottlenecks in third-party code

  • Providing additional debugging information for module users

Using Debug with Different Log Levels

Debugging with Different Log Levels

Understanding Log Levels

Log levels are used to categorize the importance of debugging messages. There are five main log levels:

  • trace: Extremely detailed information used for low-level debugging.

  • debug: Additional information for general debugging.

  • info: General information about the program's execution.

  • warn: Warnings about potential issues.

  • error: Critical errors that require immediate attention.

Example:

console.error("This is an error"); // Log an error
console.warn("This is a warning"); // Log a warning
console.info("This is information"); // Log general information
console.debug("This is debug information"); // Log debug information
console.trace("This is a trace log"); // Log detailed tracing information

Setting the Log Level

You can set the log level using the DEBUG environment variable. Set it to one of the log level names:

  • traces

  • debug

  • info

  • warn

  • error

Example:

DEBUG=info node my_script.js

Filtering Log Messages

You can use the DEBUG variable to filter log messages by module name. For example, to only log messages from the "my-module" module at the debug level or higher, set DEBUG to:

DEBUG=my-module:debug

Real-World Applications

  • Tracing: Helps identify performance bottlenecks or uncover hidden bugs.

  • Debugging: Provides detailed information to help find and fix errors.

  • Monitoring: Logs important events or performance metrics for analysis.

  • Logging: Stores debug messages for later review or troubleshooting.

Complete Code Implementations

Logging at Different Levels:

const debug = require('debug');

const logInfo = debug('my-app:info'); // Log at the info level
const logWarn = debug('my-app:warn'); // Log at the warn level

logInfo('Informational message');
logWarn('Warning message');

Filtering Log Messages:

const debug = require('debug');

const filteredDebug = debug('my-app:debug'); // Log at the debug level for the "my-app" module
filteredDebug('Filtered debug message');
PreviouscoNextdebut