Error Handling in JavaScript Projects


As a software developer, I’ve encountered my fair share of bugs and errors. It’s an inevitable part of the development process. However, what distinguishes a good developer from a great one is not just the ability to write error-free code, but the skill to handle errors effectively when they do occur. This is why I’ve decided to share my two cents on error handling in JavaScript projects.

Error handling is a critical component of any project. It ensures that your application can gracefully manage unexpected situations, maintain its functionality, and provide a seamless user experience. In this blog post, we’ll explore the various facets of error handling in JavaScript. We’ll start with the basics, such as understanding different types of errors and using the try...catch statement, and gradually move towards more advanced topics like handling token expiration and network issues.

By the end of this post, I hope you’ll have a comprehensive understanding of error handling that will elevate your JavaScript projects from merely functioning to truly robust and reliable. So, join me as we navigate the intricacies of JavaScript error handling together.

Fundamentals of Error Handling

In this section, we’ll cover the three primary types of errors you’ll encounter in JavaScript: syntax errors, runtime errors, and logical errors. Understanding these will help you write more resilient code.

Syntax Errors

Syntax errors are mistakes in the use of the JavaScript language. These are typically caught by the interpreter when it tries to compile the script. A common tool to catch these errors is ESLint, a static code analysis tool that identifies problematic patterns in JavaScript code. It can catch everything from stylistic errors to potential bugs:

// ESLint can catch simple syntax errors
const greeting = 'Hello, world'

In the example above, if your ESLint rules require a semicolon at the end of each statement, it would flag the missing semicolon after the greeting declaration.

Runtime Errors

Runtime errors, also known as exceptions, occur while the program is running. JavaScript provides a try...catch statement that allows you to handle these errors gracefully:

try {
  // Code that may throw an error
} catch (error) {
  // Code to handle the error

The try block contains the code to be executed, and the catch block allows you to define a response to any errors thrown. It’s important to use try...catch judiciously, as overuse can lead to performance issues and make the code harder to read and maintain.

Logical Errors

Logical errors occur when the code doesn’t perform as expected, but it doesn’t necessarily crash or throw an error. These are often the hardest to diagnose because the code is syntactically correct. To handle logical errors:

Write unit tests to ensure your code behaves as expected. Use debugging tools to step through your code and inspect variables. Review your logic and algorithms carefully to ensure they’re correct. Here’s an example of a logical error and how you might catch it:

function calculateArea(width, height) {
  // A logical error: using addition instead of multiplication
  return width + height; // Should be width * height

const area = calculateArea(5, 4);
if (area !== 20) {
  console.error('There is a logical error in the calculateArea function');

In the example, the calculateArea function incorrectly adds the width and height instead of multiplying them. The conditional check after the function call is a simple way to assert that the function’s output is as expected.

Advanced Error Handling Strategies

Custom Error Classes

Custom error classes in JavaScript are a powerful way to provide more descriptive error information, which can be particularly useful when debugging. By extending the native Error class, you can create your own error types that can be checked against using instance of. Here’s an example:

class ValidationError extends Error {
  constructor(message, field) {
    super(message); = "ValidationError";
    this.field = field;

function validateUser(user) {
  if (!user.username) {
    throw new ValidationError("Username is required", "username");
  // Additional validation checks...

try {
} catch (error) {
  if (error instanceof ValidationError) {
    console.error(`${}: ${error.message} at ${error.field}`);
  } else {
    throw error; // Unhandled error types are re-thrown

In the above code, ValidationError is a custom error class that captures additional context about the error, such as the field that failed validation. This makes it easier to handle specific error cases and provide more informative error messages.

Asynchronous Error Handling

With the advent of async/await in JavaScript, handling errors in asynchronous code has become more straightforward. The await keyword allows us to write asynchronous code that looks and behaves like synchronous code. Here’s how you can handle errors in an async function:

async function fetchData(url) {
  try {
    const response = await fetch(url);
    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`);
    const data = await response.json();
    return data;
  } catch (error) {
    console.error('Failed to fetch data:', error);

  .then(data => console.log(data))
  .catch(error => console.error('Error in fetchData:', error));

In this example, fetchData is an async function that retrieves data from a URL. If the fetch request fails or the server returns a non-200 status code, an error is thrown and caught in the catch block. This pattern allows for clean and easy-to-read asynchronous error handling.

Error Handling in Production

When your application moves from development to production, error handling takes on an additional layer of complexity. It’s not just about catching errors, but also about logging them appropriately, displaying user-friendly messages, and maintaining security.

Logging Errors

Effective logging in production plays a crucial role in monitoring and debugging processes. To optimize this practice, it’s important to establish clear logging objectives that align with your operational goals. This involves defining the specific information that needs to be captured by the logs. Additionally, using log levels correctly is vital; it helps in distinguishing routine events from those that necessitate immediate action. Structuring your logs in an organized manner not only facilitates easier analysis but also accelerates the resolution of issues. Lastly, safeguarding your logs is imperative to ensure that they remain free of sensitive data and are maintained in a secure environment. By adhering to these best practices, you can enhance the effectiveness of your logging strategy.

Displaying Error Messages

The manner in which errors are communicated to users is pivotal in shaping their experience. Employing clear and descriptive language that steers clear of technical jargon makes the message accessible and understandable. An empathetic tone is equally important; error messages should convey friendliness and assistance, rather than placing blame on the user. Additionally, a consistent design across all error messages within the application reinforces a sense of reliability and professionalism. By focusing on these aspects, you can significantly enhance user satisfaction and trust in your application.

Security Considerations

Incorporating security considerations into error handling is a critical aspect of production-level software development. For instance, imagine a scenario where a user attempts to access a restricted area of a web application without proper authorization. Instead of displaying a generic error message, the system should log the attempt with enough detail for internal analysis while presenting the user with a friendly but non-specific denial message. This approach prevents the exposure of sensitive information or system vulnerabilities that could be exploited by malicious entities. Furthermore, implementing robust error handling mechanisms is crucial. These should be designed to handle exceptions gracefully without providing potential attackers with clues that could be exploited to uncover security vulnerabilities.

Handling Common Runtime Errors

Network Issues

Network issues, while often inevitable, can be managed effectively to ensure a seamless user experience. For example, consider a user trying to submit a form on a web application. If the user’s internet connection drops, JavaScript’s navigator.onLine property can be used to detect this change in network status. The application can then respond by informing the user of the connectivity issue with a clear and user-friendly message: “Unable to connect. Please check your internet connection and try again.” To further assist the user, the application can disable features that require a network connection, thus preventing further errors and confusion.

Moreover, including a ‘Retry’ button provides users with the autonomy to initiate a new attempt once their internet connection is restored. This button should trigger a retry mechanism that re-attempts the failed network request. Implementing such a mechanism with an exponential backoff strategy is beneficial as it progressively increases the intervals between retries, thereby reducing the load on the server and enhancing the chances of successful reconnection.

if (!navigator.onLine) {
  displayMessage("You are offline. Please check your connection.");
} else {
  // Proceed with network request

Token Expiration

Handling token expiration is a critical aspect of user authentication. To ensure a secure and uninterrupted experience, it’s important to check if the authentication token, like a JWT, is still valid before making an API call. If it’s expired, the user should be either prompted to log in again or the token should be refreshed automatically, if your system allows for it. It’s also essential to inform the user with a clear message that their session has expired and guide them to the next step, whether that’s logging in again or waiting for the token to refresh automatically. This approach helps maintain a secure environment while keeping the user experience smooth and hassle-free.

const token = localStorage.getItem('token');
if (isTokenExpired(token)) {
    .then(newToken => {
      localStorage.setItem('token', newToken);
      // Retry the original request with the new token
    .catch(() => {
      displayMessage("Session expired. Redirecting to login page.");

And there you have it! We’ve journeyed through the landscape of error handling in JavaScript, uncovering the tools and techniques that can transform your code from fragile to formidable. From the pesky syntax errors caught by ESLint to the more elusive logical errors that test our debugging prowess, we’ve covered a lot of ground. Remember, error handling isn’t just about fixing what’s broken; it’s about anticipating the unexpected and crafting an experience that feels seamless and thoughtful to your users. It’s about writing code that’s not only functional but also resilient and secure. So, I hope you take these insights, apply them to your projects, and watch as your applications stand strong against the challenges thrown their way. Keep learning, keep coding, and most importantly, keep handling those errors like the expert you’re becoming.