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Master JavaScript Debugging: Strategies and Best Practices

Anchal Rastogi

Javascript is one of the most commonly used scripting languages used for web development. Nowadays a lot of mobile applications are also built on frameworks using javascript. It is the most commonly used framework used by developers across the world today. 

zipy - javascript usage statistics
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Javascript is most commonly used by Frontend developers. They would build applications based on javascript frameworks or libraries like react, angular, vuejs , nextjs etc.. Nowadays the backend engineers also use javascript as part of nodejs development. 

What is javascript Debugging 

Javascript debugging is the process of understanding and fixing problems found in code written in Javascript to ensure smooth working of the code or applications written in Javascript. 

Multiple tools are used to debug Javascript today. We will be sharing some of these below. 

Key Concepts in javascript Debugging

Some of the key concepts in javascript debugging are listed below. Any developer trying to solve a problem in their javascript code should have a good understanding of these concepts to be able to solve these problems. 

Error Types:  It is important that developers know the basic types of errors in Javascript. Some of the common ones are listed below. Understanding why each one of these happens and how they can be fixed is a must have for any developer. 

  • Syntax Error
  • Reference Error 
  • Type Error 
  • URI error 
  • Type Error 

Breakpoints: When debugging javascript code locally, one should be able to apply the right set of breakpoints to pause and evaluate the various variables and call stack etc. 

Call Stack: A call stack is a sequence in which the functions were called so it keeps track of the execution of the workflow. To be able to read a call stack is very important for engineers to debug an application from a workflow perspective. Here is a sample of javascript call stack trace. 

zipy - stack trace - type error
zipy - stack trace - console logs

Variable Scope: Variable scope is an important concept in Javascript. Knowing how variable scope works in JavaScript, including global scope, function scope, block scope (with let and const), and lexical scoping, helps in identifying where variables are accessible and where they might cause issues.

Console Methods: Console logs are one of the most powerful and commonly used concepts in Javascript debugging. Using  console.log, console.error, console.warn, etc. helps the developers to log the information and errors and understand the flow and also the exceptions better. They should be used in the right way to ensure that the logging is optimally used. Here is how Zipy allows you to capture console logs in Zipy. 

Debugger Statement: Using the debugger; statement within the code triggers the browser's debugger, allowing step-by-step execution and inspection of variables at that point.

Exception Handling: Handling exceptions gracefully in code with try-catch blocks  is very helpful for front-end developers. This allows the application to keep running without crashing. Logging these exceptions is also very useful. Here’s how Zipy allows you to capture exceptions in Javascript code. 

Debugging Tools: Knowing which tools to use for javascript debugging is one of the most critical learnings for a developer. Knowing how to use the Chrome DevTools or Firefox/Safari DevTools is essential. Understanding that tools like Zipy can also help you debug Javascript Debugging in minutes is the key to improving efficiency. 

Network and Performance Monitoring: While debugging a Javascript application, the developers may face issues in not just Javascript code or html/css code but also in network calls or page slowness. To debug an application, developers also need to understand how to find and fix network bottlenecks and page slowness issues. An understanding of types of network errors in browser or mobile applications and using the right set of tools for performance issues is a must have. Here is a sample network errors view. 

zipy solves api problems and network issues

Zipy helps you uncover API problems and also network issues in your Javascript application. 

Testing Strategies: Getting the right set of tools to test your application is also a key to developer productivity. RIght Javascript testing tools are a must have. Using end to end testing  tools like e Jest, Mocha, Jasmine, etc. could be very helpful to become adept at Javascript Debugging the above concepts are very important. 

Common Issues in javascript Debugging 

A crucial aspect of programming in JavaScript is - debugging. As you know, javascript debugging is the process of finding and resolving bugs or defects that prevent correct operation of computer software or a system. It's an integral part of programming. Let's discuss some common issues you might encounter while debugging JavaScript code.

Syntax Errors: This is where we start. Syntax errors are the most basic form of errors you'll encounter. They happen due to simple mistakes like missing a semicolon (;), a parenthesis, or using incorrect syntax. These errors stop your code from executing. It’s like writing a sentence with poor grammar, the JavaScript engine just can’t understand it!

Variable Scope Issues: Here's where things get tricky. In JavaScript, we have 'var', 'let', and 'const' for declaring variables. Each has its own scope rules. Misunderstanding these can lead to reference errors or unexpected behaviors in your code.

Undefined or Null Values: This is a common one. When you try to access a property or method of something that’s undefined or null, you'll run into errors. This is often seen when dealing with APIs or external data sources.

Type Errors: JavaScript is loosely typed, but that doesn’t mean it's forgiving about types. Performing operations on incorrect data types leads to type errors. For example, you can't do arithmetic operations on strings the way you do on numbers.

Asynchronous Issues: JavaScript often operates asynchronously, especially in web environments. Problems arise with race conditions or incorrect handling of promises, callbacks, or async/await functions. It’s like expecting a reply from someone before they’ve heard your question!

Scope Chain and Closures: This is a bit advanced but very important. Closures allow a function to access variables from an enclosing scope. Misunderstanding this can result in unexpected values in your variables.

Event Handling Problems: When your event listeners don't work as expected, or events are not handled properly, it disrupts user interactions like clicking a button or submitting a form.

Cross-Browser Compatibility: The web is vast and diverse. Different browsers can interpret JavaScript differently. Code that works in one browser might not work in another.

Memory Leaks: These are critical. Poor management of memory, like unnecessary references or not releasing resources, can lead to performance issues or even crash your application.

Third-Party Libraries or APIs: Using external libraries or APIs can be tricky. Integration issues, incorrect usage, or relying on outdated versions can create unexpected bugs.

Debugging DOM Manipulation 

When debugging DOM manipulations in JavaScript, you may encounter a range of common issues. It is essential to understand these issues and how to address them for efficient debugging. Here are some of the typical problems developers face when working with DOM manipulations:

Selecting the Wrong Element: Selecting the correct DOM element is crucial for successful manipulation. If you select the wrong element or an element that does not exist, your code won't work as expected. So double-check your selectors and use the browser's developer tools to inspect the selected element.

const elementToBeManipulated = document.getElementById('testElement'); if (elementToBeManipulated) { // Do manipulations here } else { // Log the error or do nothing }

Timing Issues: If DOM manipulations execute before the DOM is fully loaded, it may lead to errors. So ensure that your DOM manipulation code runs after the DOM is ready and to handle that you can use event listeners like DOMContentLoaded to guarantee that the DOM is accessible.

document.addEventListener('DOMContentLoaded', function() { // Add your DOM manipulation code here });

Event Handling Issues: Managing event handlers can be tricky, especially when dealing with dynamically created elements or nested event listeners.

To solve or reduce such issues, you can delegate events by attaching event listeners to a higher-level parent element and using event delegation to handle events for child elements. This way, dynamically created elements will still be covered.

Browser Compatibility: Different browsers may interpret the DOM and events differently. It might happen that the code that works perfectly in one browser may fail in another.

Hence, cross browser testing is essential if you plan to support multiple browsers. You can use feature detection or polyfills to ensure cross-browser compatibility.

Asynchronous Behavior: Most of the network requests - AJAX or Fetch often work asynchronously, and due to that there may be cases when some DOM manipulations do not complete before the next line of code executes. To make sure that these scenarios don’t occur with your code, use callbacks, promises, async/await, or the .then method to ensure that your code waits for asynchronous operations to complete before proceeding.

async function fetchDataAndRender() { try { // Fetching data from an API const data = await fetchDataFromAPI(); // Update the DOM with the fetched data } catch (error) { console.error('Error fetching data:', error); } } function fetchDataFromAPI() { // Simulated API call with a delay return new Promise((resolve) => { setTimeout(() => { // Simulated data const data = { message: "Hello, world!" }; resolve(data); }, 2000); // Simulating a delay of 2 seconds }); }

Inconsistent State Updates: If you are updating the DOM based on application state, inconsistencies can arise if the state is not correctly managed.

Implement a state management system or use a framework (e.g., Redux, MobX, or a front-end framework like React or Vue) to ensure consistent state updates and their reflection in the DOM. To effectively debug these issues, use Dev tools provided by these libraries like Redux, to check and verify the state values being set at runtime.

HTML and CSS Validation: Sometimes, issues in DOM manipulations are due to invalid HTML or CSS. Hence validate your HTML and CSS using tools or browser developer tools to ensure that the structure and styles are correct.

Performance Bottlenecks with inefficient DOM updates: Frequent updates to the DOM can impact performance. Inefficient DOM updates can cause slow rendering and increased memory usage especially when dealing with large datasets or complex UIs, say for graphs and dashboards.

These can be debugged using Page Performance analytics provided by tools like Zipy to pinpoint the exact problem areas. 

You can minimize reflows and repaints, and use techniques like virtual DOM (in frameworks like React) to reduce unnecessary DOM changes.

zipy effective javascript debugging

By being aware of these common issues, you can streamline the debugging process when working with DOM manipulations in JavaScript. Effective javascript debugging not only resolves issues but also contributes to the creation of performant and reliable web applications.

Debugging AJAX and Fetch Requests

Http requests can be made using both fetch() and Axios, but they have different features and syntax. 

Fetch API:

  • Built-in: fetch() is a built-in browser API for making HTTP requests introduced in modern JavaScript.
  • Syntax: Promise-based syntax.
  • Basic Usage: Here's a basic fetch() example:


fetch('') .then(response => { if (!response.ok) { throw new Error('Network response was not ok'); } return response.json(); }) .then(data => { console.log(data); }) .catch(error => { console.error('There was a problem with the fetch operation:', error); });


  • Library: This is a third-party library designed for making HTTP requests in both browser application and Node.js environments. 
  • Syntax: Axios uses a promise-based syntax similar to fetch(), but it offers more features and a simpler API.
  • Basic Usage: Here's an example using Axios:


axios.get('') .then(response => { console.log(; }) .catch(error => { console.error('There was a problem with the Axios request:', error); });

Differences in Error handling in Axios and fetch:

Let’s compare error handling and debugging techniques in two popular methods of making HTTP requests in JavaScript: Axios and Fetch. Understanding these differences is key to writing robust web applications.

Differences in Error Handling

Axios vs Fetch:

Axios automatically rejects promises on HTTP error status codes like 404 or 500. This means if your server responds with an error status, Axios treats this as a rejection.

Fetch, however, does not automatically reject HTTP errors. You need to manually check the ok property of the response. If it’s false, it indicates an HTTP error.

Canceling Requests:

Axios has built-in support for canceling requests using cancel tokens.

Fetch lacks native support for request cancellation.

Debugging Fetch Requests

  • Using Network Tab: Use your browser’s developer tools and inspect the Network tab. This helps in examining request/response details, such as status codes, headers, and payloads.
  • Handle Promise Rejection: It's crucial to handle errors in your fetch() chain. Here’s a sample code demonstrating this:
fetch('') .then(response => { if (!response.ok) { throw new Error('Network response was not ok'); } return response.json(); }) .then(data => { console.log(data); }) .catch(error => { console.error('Some problem with the request:', error); });
  • Logging and Debugging: Use console.log() to log request/response details, especially within the .catch() block for any caught errors. For more effective debugging, you can response details like status and payload and error stacktrace.

Debugging Axios Requests

  • Axios Interceptors: You can use Axios interceptors for handling request and response errors. They should be placed in global handlers:
axios.interceptors.response.use( response => response, error => { console.error('There was an Axios request error:', error); return Promise.reject(error); } );
  • Response Object:

You can access more details of network requests in Axios through the error object:

axios.get('') .then(response => { console.log(; }) .catch(error => { if (error.response) { console.error('Server responded with a non-2xx status:', error.response.status); } else if (error.request) { console.error('Request was made but no response was received'); } else { console.error('Error in setting up the request:', error.message); } });
  • Network Tab and Logging:

Similarly to fetch, you can use the browser's Network tab to view requests and responses. Adding logs can help track the flow of Axios requests and responses.

By understanding these differences and leveraging tools like browser dev tools, error handling methods, and logging, you can effectively debug and handle failures in fetch() or Axios requests in your JavaScript applications. This knowledge is essential for identifying and resolving issues quickly and efficiently.

Debugging JavaScript Frameworks (React, Angular, Vue, etc.)

Javascript debugging varies slightly among different frameworks or libraries due to their unique architectures and tooling. Here's a general comparison of debugging approaches for React, Angular, Vue.js, and Next.js applications:


React DevTools:

  • React offers a handy browser extension known as React DevTools. This tool is invaluable for inspecting the component hierarchies, state, and props in your React applications. Imagine it like having a magnifying glass that lets you zoom in on each component of your React app, understanding how they interact and hold data. There are other react debugging tools that can be used based on an individual’s preference and targeted use cases.

Error Boundaries:

  • React introduces a concept called Error Boundaries. These are like safety nets that catch JavaScript errors in a component and display a fallback UI instead of crashing your entire application. When you're debugging, setting up Error Boundaries helps you isolate and handle errors more effectively. It's like having a first-aid kit for your components – it won't prevent the accident, but it helps manage the damage!

Use of JavaScript Debugging Tools:

  • Traditional JavaScript debugging tools, such as console.log(), the debugger statement, and browser developer tools, are also crucial in React. They help in inspecting state changes, tracking data flow, and understanding the logic behind your application. These tools are your bread and butter for digging into the nitty-gritty of your React app's behavior.

Zipy Debugging: 

  • Use Zipy to understand and debug QA and production issues. Zipy catches all errors, console logs, network requests, response and performance issues by default for React applications. 



  • Augury is a Chrome extension specifically designed for Angular applications.
  • It provides a visual representation of your application’s component tree. This is incredibly useful for understanding the structure and hierarchy of your Angular components.
  • Augury also allows you to inspect dependencies, router states, and more, making it easier to debug issues related to Angular’s complex architecture.

Angular DevTools

  • Angular DevTools is another tool that helps in inspecting components and services within an Angular application.
  • It also provides insights into the application’s performance, which is crucial for optimizing your app and enhancing user experience.

Zone.js Debugging:

  • Angular uses Zone.js for managing tasks such as change detection and error handling.
  • When debugging Angular apps, it’s important to understand how Zone.js interacts with your application.
  • Issues often arise in the context of asynchronous tasks, and Zone.js plays a key role in tracking those tasks and triggering change detection.
  • Debugging might involve troubleshooting issues related to Zone.js, such as unexpected behavior in asynchronous operations.

RxJS Debugging:

  • RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using observables.
  • In Angular, RxJS is often used for managing data streams and handling asynchronous tasks.
  • Debugging RxJS observables involves understanding how data flows through these streams and how different operations affect the data.
  • A common challenge is debugging subscription-based code. It’s crucial to ensure that observables are properly subscribed and unsubscribed to avoid memory leaks and other performance issues.

Zipy Debugging: 

  • Use Zipy as an angular debugger to understand and debug QA and production issues. Zipy catches all errors, console logs, network requests, response and performance issues by default for Angular applications. 


Vue DevTools- A Browser Extension:

  • Vue.js offers a powerful tool called Vue DevTools, which is a browser extension.
  • It's designed to help you inspect and debug Vue applications.
  • With Vue DevTools, you can easily visualize and interact with your Vue component tree. This includes inspecting components, their props, data, events, and more.

Using Vue DevTools for Debugging:

  • When debugging Vue applications, Vue DevTools becomes an invaluable asset.
  • You can use it to see real-time changes in component states and props. This live feedback is incredibly helpful for understanding how data flows through your application.
  • It also allows you to manipulate the state and props of components directly from the DevTools, offering a practical way to test and debug component behavior.

Vue CLI:

  • The Vue Command Line Interface (CLI) provides a standard tooling setup for Vue applications.
  • It simplifies the process of starting, developing, and building Vue applications.

Built-in Tooling:

  • Vue CLI comes with built-in tooling that greatly aids in the debugging process.

Hot Reloading: This feature automatically reloads your app or component when you make changes to the code. It saves time and helps you immediately see the effects of your changes.

ESLint Integration: Vue CLI integrates ESLint, a tool for identifying and reporting on patterns in JavaScript. It helps catch errors and enforce coding standards, making your code more robust and consistent.

Error Handling: Vue CLI provides helpful error handling during the development process. It displays errors in a clear and understandable way, often with suggestions for fixing them.

Use Zipy for Debugging: Zipy monitors and catches all errors, console logs, network requests, response and performance issues by default for Vuejs applications. So you can use Zipy as a debugging tool to understand and debug QA and production issues.

Next.js (React-based):

Next.js DevTools and React DevTools:

  • Next.js applications can be debugged using both React DevTools and specific Next.js DevTools.
  • React DevTools is a browser extension that helps you inspect the React component hierarchies in your application. It's great for understanding the state and props of your components.
  • Next.js DevTools, on the other hand, offer more specific insights into Next.js features. This includes data fetching methods, page rendering strategies, and more.

Using DevTools for Debugging Next.js

  • When debugging Next.js apps, it's important to look at how server-side rendering and static generation are being handled.
  • These DevTools can help you understand how your pages are rendered and how data is fetched and used in your application.

Hydration and SSR Debugging:

  • Client-Side Hydration of Server-Rendered Content:Hydration is the process where a client-side JavaScript picks up where server-side rendering left off.Debugging hydration issues can be tricky. It involves ensuring that your server-rendered HTML is correctly being enhanced with client-side interactions.
  • Data Fetching and SSR-Related Errors:Inconsistencies in data fetching, especially when data is fetched during server-side rendering, can lead to errors or unexpected behaviors.Debugging these issues often requires a deep dive into how Next.js handles data fetching on both the server and the client side.
  • Strategies for Debugging SSR Issues:Pay close attention to how your application behaves on the server versus the client. Look for discrepancies that might hint at hydration problems.Use server logs and client-side console logs to gather information about errors and the application's state at different stages.

Zipy Debugging: 

  • Use Zipy as a nextjs error and performance monitoring tool to understand and debug QA and production issues. Zipy catches all errors, console logs, network requests, response and performance issues by default for Next.js applications.

Common Aspects:

Browser Developer Tools:

  • Importance of Browser Developer Tools
  • Tools like Chrome DevTools are indispensable for any web developer. 
  • These tools allow you to inspect network requests, view console logs, track JavaScript errors, and analyze the performance of your web applications.
  • Key Features of Browser Developer Tool:
  • Network Tab: This is where you can monitor network activity, inspect HTTP requests and responses, and troubleshoot network-related issues.
  • Console: The console is essential for viewing log statements and errors. It's also a place where you can execute JavaScript code directly.
  • Sources Panel: Here, you can set breakpoints, step through your code, and inspect variables to understand how your code is executing.
  • Performance Tab: This section provides tools to analyze the runtime performance of your application, helping you identify bottlenecks.

Logging and Debugging Techniques:

  • Logging with console.log():One of the simplest, yet effective, debugging techniques is to log information to the console. This can help you track the flow of your application and inspect the state of your data.
  • Setting Breakpoints:Breakpoints allow you to pause your code at specific points. You can set them in your browser's Sources panel. This is incredibly useful for examining the state of your application at critical moments.
  • Using the debugger Statement: Adding the debugger statement in your code will cause the browser to pause execution at that point, similar to a breakpoint. This is useful for temporary debugging during development.
  • Employing Error Handling:Proper error handling, using try-catch blocks, ensures that your application can gracefully handle exceptions and errors. It also provides a means to understand and resolve issues.
  • Debugging with tools like Zipy: Irrespective of the underlying Javascript framework or library used, Zipy helps you debug the most complex Javascript errors, fetch or Axios failures, Performance issues and much more. 

Each framework or library has its own set of debugging tools and strategies tailored to its specific architecture and features. However, the fundamental debugging principles—understanding error messages, utilizing developer tools, and employing debugging techniques—remain consistent across these ecosystems.

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Debugging Performance Issues

A performance issue in a JavaScript application refers to any aspect of the application that causes it to run slower or less efficiently than desired, impacting user experience. These issues can manifest in various ways and affect different parts of the application. Here are some common performance issues in JavaScript applications:

Slow Rendering:

  • When the application takes longer to render UI elements, causing delays in displaying content or updating the interface in response to user interactions.

Excessive DOM Manipulation:

  • Frequent and inefficient updates to the Document Object Model (DOM) can lead to performance degradation, especially when manipulating large sets of elements or triggering layout recalculations

Memory Leaks:

  • Improper handling of memory resources, such as not releasing unused objects, event listeners, or closures, can result in memory leaks, gradually slowing down the application and potentially causing crashes.

Inefficient JavaScript Code:

  • Poorly optimized code, such as inefficient algorithms, excessive loops, redundant calculations, or unnecessary function calls, can significantly impact the application's performance.

Network Latency:

  • Issues related to network requests, such as slow API responses, excessive data fetching, or large file sizes, can contribute to performance bottlenecks, especially in web applications relying on external resources.

Inefficient Data Processing:

  • Heavy computations or complex data manipulations performed in JavaScript can strain the application's performance, particularly when handling large datasets or running operations synchronously.

Excessive Event Handlers:

  • Too many event listeners or poorly managed event handling can cause performance issues, especially when numerous interactions trigger complex operations.

Inadequate Caching and Optimizations:

  • Lack of caching strategies or optimization techniques, such as lazy loading of resources, bundling, code-splitting, and minimizing redundant requests, can impact the application's loading speed and responsiveness.

Poor Browser Compatibility:

  • Compatibility issues across different browsers or devices might result in performance variations, leading to sluggish behavior on specific platforms.

Addressing performance issues in JavaScript applications often involves:

  • Profiling and identifying bottlenecks using browser developer tools and performance monitoring tools.
  • Optimizing critical code segments, minimizing DOM manipulations, and adopting best practices for efficient data handling.
  • Implementing caching strategies, optimizing network requests, and improving resource loading techniques.
  • Utilizing performance analysis tools, adopting modern JavaScript features, and considering code splitting and lazy loading for larger applications.

Improving performance requires a combination of careful analysis, code optimization, utilizing appropriate tools, and adhering to best practices throughout the development process.

Best Practices and tips for javascript Debugging 

Debugging Workflows and Methodologies 

Javascript Debugging is a critical aspect of the software development process for any web application, and over the years there are various workflows and methodologies that have evolved which can be applied to effectively debug JavaScript applications. Here are some common debugging workflows and methodologies that can be used for JavaScript apps:

Interactive Debugging:

Workflow: Interactive javascript debugging is an iterative and hands-on approach. Developers use browser developer tools or integrated development environments (IDEs) to set breakpoints, inspect variables, and step through code.

Methodology: Developers identify specific issues, set breakpoints where they suspect problems, and gradually step through the code to understand how it executes. They examine variable values and control flow to pinpoint the root cause of issues.

Console-Driven Debugging:

Workflow: Console-driven javascript debugging relies heavily on logging messages and variable values to the console using console.log(), console.error(), and other console methods.

Methodology: Developers add console statements strategically throughout the code to log values, messages, and control flow information. They analyze the console output to trace the code's execution and identify issues.

Test-Driven Development (TDD):

Workflow: TDD is an approach in javascript debugging where developers write tests before implementing features. When tests fail, they debug to make the tests pass.

Methodology: Developers create unit tests and integration tests that define the expected behavior of code. When a test fails, they debug the code to address the failure and continue this cycle iteratively. Tools like Jest, Mocha are used widely to get the code coverage and discover problems early on.

zipy test driven development

Static Analysis:

Workflow: Static analysis tools examine the code without executing it. These tools analyze code for issues, such as syntax errors, code style violations, unused variables and potential security vulnerabilities.

Methodology: Developers use tools like ESLint, JSHint, or TSLint to perform static code analysis which can be easily integrated with any developer environment. It is good to have a process defined around the usage and strict guidelines on code releases post these issue resolutions to ensure code quality is maintained and there are lesser problems in the production environment.

Performance Profiling:

Workflow: Performance profiling is a way to monitor the execution of JavaScript code to identify performance bottlenecks and resource-intensive operations.

Methodology: Developers use profiling tools like the Performance tab in browser developer tools to identify slow functions, memory leaks, and excessive rendering. The code can then be optimized based on profiling results and suggestions provided to improve app performance.

Behavior-Driven Development (BDD):

Workflow: BDD focuses on defining desired behaviors before writing code. Developers use BDD frameworks to specify behavior of an application in a human-readable format.

Methodology: Developers create behavior specifications using tools like Cucumber, Jasmine, or Mocha. The code is then implemented to meet these specifications, ensuring alignment with the desired behavior.

User Testing and Feedback:

Workflow: Real users of the application provide feedback on its behavior, usability and report issues.

Methodology: Developers release a version of the app (generally alpha or beta) for user testing and collect user feedback, bug reports, and usage data to identify and prioritize issues. They can also use feedback to reproduce and resolve problems as well.

Error Monitoring and Logging:

Workflow: Error monitoring tools like Zipy collect and aggregate errors and exceptions from production environments and serve as right hand in javascript debugging.

Methodology: Developers use tools like Zipy, Sentry, New Relic or Rollbar to monitor errors and exceptions in the live application. These tools provide all the information related to an issue to help prioritize, analyze and diagnose critical issues, leading to quicker resolutions and deployments to production as needed.

zipy - error monitoring tool

Each of these debugging workflows and methodologies has its place in the software development process. Depending on the context and nature of the issues, developers may choose one or more of these approaches to effectively identify and resolve problems in JavaScript applications.

Real-Device vs. Emulator Testing 

Though most of the Javascript app testing is done on real devices, there can be cases where emulator testing becomes important to ensure the application supports a wide range of devices and browsers without any breakages or user experience issues.

Some of the best practices while performing device testing are mentioned as follows.

Automate Testing:

Use automated testing frameworks as much as possible to enable easy cycle runs post every release or change. Tools like Selenium, Appium, or Cypress can be utilized to create test scripts that cover common user interactions and scenarios and to run tests on both real devices and emulators.

Cross-Browser Testing:

Perform cross-browser testing to identify and fix issues specific to different browsers. You can use tools like BrowserStack, CrossBrowserTesting, and Sauce Labs that provide access to a wide range of mobile devices and browsers and can help automate cross-browser testing.

Many times, the issues found during javascript debugging are due to different features supported/differently supported in browsers.

Emulate Real Network Conditions:

Emulate different network conditions (e.g., 3G, 4G, slow connections) to test how your app performs under various network constraints.

Most browsers have built-in developer tools that allow you to throttle the network speed and test your app on different device emulations  and network conditions.

Accessibility Testing:

Ensure your app is accessible to users with disabilities by conducting accessibility testing on both real devices and emulators.

Use accessibility testing tools like Axe, pa11y, or Lighthouse to identify and fix accessibility issues.

Apart from these, it is also important to follow  responsive design principles while building your app to ensure it adapts to various devices and screen sizes, delivering a consistent and reliable user experience.

Version Control Integration

Version control systems can help in javascript debugging in various ways.

Utilizing CI/CD Setup:

CI (Continuous Integration)/CD(Continuous Delivery) processes automatically build, test, and deploy code to production. Most of the version control systems like GitHub have CI/CD hooks and you can use external tools like Jenkins to build an automated CI/CD pipeline as well. It is important though that most of the sanity testing is automated in this case. Code analysis tools can also be integrated with these systems to provide feedback on code quality and correctness along with manual peer reviews. 

Branching and Experimentation:

When debugging, developers can create a new branch to isolate the issue and test potential fixes without disrupting the rest of the development process.

Code Comparison

Developers can compare different versions of the code, making it easier to identify what code changes may have introduced bugs. By comparing the current code with a previous working version, developers can isolate the changes and focus their debugging efforts more effectively.

Change Reverts:

In case of issues with the new release, VCS can be used to quickly revert the changes when possible and deploy a previous code base to production. Developers can then take time to debug the problem and provide the required solution without worrying about the user impact. 

Collaborative Debugging and Issue Resolution

Sometimes it is imperative to include another eye for javascript debugging in case you are the developer and have made the changes that might be causing the issue in production. Code reviews, pair programming, peer testing are some of the ways by which this can be achieved.

Code Review:

Developers collaborate by reviewing each other's code, suggesting improvements, and identifying issues. This helps in identifying issues proactively before the code is pushed for QA. These also help with shared best practices amongst the team. 

Pair Programming:

In pair programming, two developers work together on the same code, with one writing code and the other providing real-time feedback and assistance.

This helps in resolving issues faster and promotes sharing of knowledge within the team.

While debugging complex issues, it is good for developers to leverage the expertise of their teammates by discussing probable solutions to the issue, sharing code snippets, and reviewing each other's changes.

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Javascript Debugging and error handling

Remote Debugging in Production 

Remote JavaScript debugging in a production environment is a valuable technique for diagnosing and resolving issues without disrupting your live application. Here are the steps to go about doing remote JavaScript debugging in a production environment:

Prepare Your Development Environment:

Ensure that you have a development environment set up with the necessary tools for remote debugging. You'll need a code editor or IDE, browser developer tools, and a reliable text editor.

Source Maps:

Before deploying your application to production, generate and include source maps. Source maps link the minified or transpiled production code to the original source code, making it easier to debug.

Production Monitoring Tools:

Implement production monitoring tools that provide real-time insights into your application's performance and error occurrences. Tools like Zipy, New Relic or Raygun can help you identify issues as they happen.

Remote Debugging Tools:

Use remote debugging tools provided by modern browsers, such as Chrome DevTools, Firefox Developer Tools, or Microsoft Edge DevTools. These tools often support remote debugging through browser extensions or cloud-based services.

Enable Remote Debugging:

In your production environment, enable remote debugging for your JavaScript code. You can typically do this by including a specific query parameter in the application's URL or by opening a dedicated debugging port.

Secure Access:

Ensure that remote debugging access is secure and restricted to authorized personnel only. Use authentication, authorization, and encryption to protect access to your live application.

Establish a Secure Tunnel:

To securely access the debugging endpoint in production, you can establish a secure tunnel using tools like ngrok, localtunnel, or SSH tunneling. This allows you to connect your local development environment to the production environment securely.

Start the Debugging Session:

Use your browser's developer tools to connect to the remote debugging endpoint. Provide the appropriate URL or connection details to establish the connection.

Inspect and Debug:

Once the connection is established, you can start inspecting and debugging your live application as if it were running on your local development machine.

You can set breakpoints, examine variables, step through code, and analyze network requests and responses.

Real-Time Feedback:

Real-time debugging allows you to see issues and their context as they occur in the live environment. This makes it easier to diagnose issues that are challenging to replicate in a local development setup.

Console Logging:

Use console.log(), console.error(), and other console methods strategically to log important information in real-time during remote debugging. These logs will be visible in the remote debugging environment.

Disable Remote Debugging:

Once you've resolved the issues and no longer require remote debugging, disable the remote debugging access to maintain security and minimize the potential for unauthorized access.

Remote JavaScript debugging in production can be a powerful tool for maintaining the health and performance of your live application. By using secure and authorized access, you can effectively investigate and fix issues in real-time without the need to replicate complex production environments locally.

Handling Critical Issues in Production 

Javascript debugging in a production environment requires a systematic approach to quickly diagnose, mitigate, and resolve problems to minimize the impact on the users. Most of the time, teams spend a lot of their effort and time analyzing and diagnosing the root cause of customer issues with less data available on hand and much back and forth between teams. 

Hence it is important to optimize this process as much as possible to ensure quick resolutions and customer satisfaction, especially if these are critical issues blocking the users. It is paramount in such situations to use appropriate tools - monitoring and logging services for logs, stack traces, user actions, and ensure your team has all the data required at hand. 

A few steps that are involved while handling critical issues in production are listed below

Identify and prioritize the Issues: Monitor production systems and user feedback to quickly identify critical issues and prioritize as critical, medium or low based on its impact on users. Zipy helps in this step of javascript debugging, in ensuring all relevant data for issue resolution is captured and available to understand the impact of the problem and also to debug and fix the issue.

Communicate with all stakeholders about the issue and the status, including your development team, product managers, and customer support. Effective communication is essential to coordinate efforts and manage expectations across. With Zipy, you can send alerts for critical issues faced by your users and also, view analytical data around the issues reported with custom slice and dice. 

Try to reproduce the issue in a controlled environment, such as a staging or development server. It’s easier to get to the root cause once you have replicated the problem in most of the cases.

Analyze the problem by isolating the issue to the affected areas or components of your application by reviewing logs, stacktraces  and any data collected by the system and subsystems. 

Use javascript debugging tools provided by the browser or 3rd parties to inspect variables, console logs, and execution flows that are relevant to the issue to get to the root cause.

Once the root cause is identified, fix the problem either with a hotfix or a permanent solution depending on the time and effort required. Ensure proper code review and regression testing is done before deployment to production so as to not break any working flows with the hotfix. 

After deployment, it is very important to verify that the fix effectively resolves the issue by testing and monitoring the application in the production environment. One important part of javascript debugging is to continuously monitor logs and error reports to ensure the problem is no longer occurring.

If required, update any support documentation and internal team documentation with the analysis, cause and resolution. This helps maintain a record as well as guide the team for similar occurrences in future. Also, communicate the status and resolution with the affected users to reassure them that the issue is fixed.

An important step in javascript debugging, which is generally missed out is having a review with your team after issue resolution, to understand gaps in the process and to identify areas for improvement like enhanced testing, improved monitoring, and stricter code reviews, and take corrective actions to prevent similar issues in the future.

Javascript debugging in a production environment for critical customer issues is very challenging due to the time constraint and varied scenarios. Hence it is important for teams to have an efficient process around it and use proper analytical tools like Zipy to reduce the time for identification and resolution of such issues. 

Pick a error monitoring and debugging tool for your needs

Check the tools

Debug javascript example

function calculateSum(a, b) { // Add a breakpoint here to debug the function let result = a + b; return result; } function main() { let num1 = 5; let num2 = "10"; // This should be a number // Adding a console.log statement for tracking variables console.log("Starting calculation..."); let sum = calculateSum(num1, num2); // Adding a console.log statement to display the result console.log("Sum:", sum); // Intentional error for debugging let undefinedVar = someVariable; // The rest of your code here console.log("End of the program."); } main();

In this example, we have a simple JavaScript program that calculates the sum of two numbers. It also intentionally introduces an error to demonstrate debugging. Here's how you can debug it using browser developer tools:

  • Open your HTML file containing the JavaScript code in a web browser.
  • Right-click on the web page and select "Inspect" or press F12 or Ctrl+Shift+I (or Cmd+Option+I on Mac) to open the developer tools.
  • Go to the "Sources" or "Debugger" tab (the name may vary depending on the browser).
  • Set breakpoints by clicking on the line numbers (e.g., the line with let result = a + b;) in the calculateSum function.
  • Start the program by reloading the web page or executing the main function in the console.
  • As you execute the program, it will pause at the breakpoints, allowing you to inspect variable values, step through the code, and diagnose any issues.
  • You can also use the console to display variable values and messages, as shown in the example. For instance, you can type num1 and num2 in the console to see their values.
  • The intentional error (let undefinedVar = someVariable;) will also cause an error that you can diagnose using the developer tools.
  • Remember to remove breakpoints and debug statements when you're done with debugging in a production environment. This example illustrates the basic process of debugging JavaScript code using browser developer tools.

Security and Data Privacy in JavaScript Debugging

JavaScript debugging, especially in the production environment, can introduce security and data privacy concerns. It's important to be aware of these issues and take appropriate measures to handle them in case an incident occurs. Here are some common security and data privacy concerns related to JavaScript debugging and ways to address them:

1. Sensitive Data Exposure:

Concern: Debugging may reveal sensitive information, such as user data, API keys, or server-side configurations, in console logs or debugging tools being used.

Mitigation: Avoid logging sensitive data in production code. Use a secure environment variable management system to store and retrieve sensitive information like passwords or keys.

Implement server-side filtering or scrubbing to prevent sensitive data from being exposed to the client-side code.

Encrypt sensitive data before storing or transmitting it.

2. Cross-Site Scripting (XSS) Vulnerabilities:

Concern: Injected scripts in console logs or error messages can lead to XSS attacks if executed in a user's browser.

Mitigation: Sanitize and validate user-generated content to prevent script injection.

Limit the exposure of debugging tools in production environments. Disable or restrict their use for non-privileged users.

Use Content Security Policy (CSP) headers to mitigate the risk of XSS attacks.

3. Data Leaks Through Error Messages:

Concern: Detailed error messages and stack traces can reveal sensitive information and code structure to potential attackers.

Mitigation: In production, configure your application to log only necessary information while avoiding detailed error messages. 

Implement error handling routines that provide user-friendly error messages without exposing internal implementation details.

4. Unauthorized Access to Debugging Tools:

Concern: Unauthorized users gaining access to browser developer tools or debugging endpoints can potentially exploit vulnerabilities.


Secure debugging endpoints with authentication, authorization, and access controls.

Limit access to debugging tools in production to only authorized personnel.

Implement rate limiting to prevent brute force attacks on debugging endpoints.

5. Code Exposure and Intellectual Property:

Concern: Javascript Debugging tools like in Browsers, may allow access to your source code, which can expose your intellectual property.


Avoid exposing your entire codebase in production environments. Minimize what's accessible through debugging tools.

Employ code obfuscation and minification techniques to make reverse engineering more difficult.

6. Privacy Violations:

Concern: Debugging tools can potentially access and leak user information or user behavior data, violating user privacy.


Always respect user privacy and adhere to relevant data protection regulations (e.g., GDPR, CCPA).

Implement data anonymization techniques to protect user privacy when collecting and logging data.

7. Data in Transit Security:

Concern: Data sent between the client and debugging tools can be intercepted if not properly secured.


Use secure connections (HTTPS) for all data transmissions between the client and debugging tools.

Implement end-to-end encryption for data to protect it from interception.

In general to avoid any of the above security concerns, 

  • Conduct Regular Security Audits:
  • Conduct regular security audits and penetration testing to identify potential vulnerabilities in your debugging infrastructure.
  • Stay updated about the latest security best practices and vulnerabilities related to debugging tools.
  • Define a Incident Response Plan:
  • Develop an incident response plan that includes procedures for handling security incidents related to debugging, such as unauthorized access or data exposure.
  • Train your team to respond to security incidents promptly and effectively.

Ensuring the security and data privacy of your applications during Javascript debugging requires a combination of secure coding practices, access controls, and adherence to data protection regulations. Regular security assessments and ongoing monitoring are essential for mitigating risks associated with debugging in a production environment.


Overall, to conclude, there are a lot of approaches, best practices and tools that can be used for javascript debugging. It depends on the application type, project development style and environment, frameworks and individual experience and preference on what to use in different scenarios. All these methodologies and tools help project teams solve problems in a reactive manner to ensure the broken customer experience is solved for and fixed. 

Now with Zipy as a javascript debugger, you can not only fix issues that are reported by your customers quickly, but can solve bugs and breakages proactively. This helps in better customer support, happy customers and reduces silent churns by a great margin.

Try Zipy to analyze and fix your production issues in real time.

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Frequently Asked Questions

If you have any more questions feel free to reach out to us at 

What is debugging in javascript?

Debugging in JavaScript involves activating built-in debuggers, which can be toggled on and off to trigger error reporting to the user. These debuggers offer the capability to set breakpoints at specific points in the code, where execution halts, allowing scrutiny of variables during runtime. Furthermore, Zipy facilitates the capture of JavaScript errors within your application, supplying pertinent stack traces and logs. This proactive approach aids in swiftly identifying and rectifying issues during the debugging process.

Is debugging JavaScript hard?

Although often perceived as a daunting task, debugging JavaScript doesn't have to be an insurmountable challenge. With a few savvy techniques at your disposal, tackling errors and bugs can become a far less time-consuming endeavor. And enter Zipy as your ultimate ally for troubleshooting, javascript debugging becomes a cake walk. By swiftly capturing any JavaScript errors within your application along with pertinent stack traces and logs, Zipy empowers you to tackle issues proactively and expedite the debugging process with ease. Say goodbye to the perplexity of unresolved bugs and embrace the burstiness of efficient problem-solving with Zipy by your side.

How to debug javascript in chrome?

To debug JavaScript in Chrome, you can use the built-in developer tools provided by the browser. First, open the webpage you want to debug in Chrome. Then, right-click on the page and select "Inspect" from the context menu to open the Developer Tools panel. In the Developer Tools panel, navigate to the "Sources" tab, where you can view and debug your JavaScript code. You can set breakpoints by clicking on the line number where you want to pause execution, and then refresh the page to trigger the breakpoint. Additionally, you can use the Console tab to log messages and interact with your JavaScript code in real-time. This process allows you to effectively diagnose and fix any issues with your JavaScript code running in Chrome. By utilizing these features and controls in Chrome Developer Tools, you can do effective javascript debugging, identify issues, and optimize the performance of web applications.

What is js debug log?

In javascript debugging, a debug log is any message that a developer wants to push onto the browser console for identifying exact problems with the code. The message can contain any specific information, objects, values that would help in tracking the flow, or error objects and stack traces to help debug the issue. You can use console.log(), console.debug(), console.error() statements to log information.

What is the best JavaScript debugger?

In the world of JavaScript debugging tools, Zipy stands out as a premier solution. Zipy is easy to use and offers unique capabilities in swiftly identifying and rectifying JavaScript errors with features like AI Resolve. It excels in real-time error detection within your application. What distinguishes Zipy is its comprehensive approach to error analysis, capturing essential details such as stack traces, logs, and the user's environment. With Zipy, the process of analyzing and resolving issues is greatly streamlined, facilitating efficient debugging and minimizing downtime.

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