In an ideal scenario, you build your APIs and backend services, deploy them to production, then sit back and relax while others use them. Unfortunately, in the real world, the programs you write will almost certainly contain errors and bugs.

For this reason, when developing Express.js APIs and backend services, it's important to factor in how different errors might occur and how to handle them effectively.

By anticipating such scenarios, you can ensure that your apps not only handle failures effectively but also provide users with a seamless experience.

Common Types of Errors in Express.js Applications

When developing Express.js applications, you'll encounter various types of errors, including:

1. Syntax and runtime errors: Syntax errors occur when there are mistakes in the code's syntax, meaning the application cannot run. Runtime errors, on the other hand, occur when the program is running, typically due to unexpected conditions or incorrect data.
2. Input validation and user errors: These errors occur when users provide insufficient or invalid data during interactions with the application. These errors can manifest in various forms, such as missing required fields, incorrect data formats, or values that do not meet specific criteria.
3. Database and network-related errors: Database and network-related errors can occur when there is a problem connecting to a database or when communication with external applications over the network fails. These errors can be particularly troublesome if your application relies on the network to operate.
4. Third-party API and service errors: Errors can also arise when interacting with external APIs or services. When making requests to external systems, various issues may arise. For example, the API might experience downtime, return responses with errors due to invalid parameters, or return unexpected data formats.

There are various techniques you can use to effectively handle errors in your Express.js REST APIs and backend services.

1. Catching and Logging Errors to the Console

A straightforward way to handle errors is to catch them and log the details to the console. This approach helps you identify errors during the development and debugging phases.

By using console.error(), you can gain insights into the nature and location of errors within your application. Here is a code example:

 app.get('/example', (req, res) => {
  try {
    // Code that may cause an error
    const result = someFunction();
    res.json(result);
  } catch (error) {
    console.error('Error occurred:', error);
    res.status(500).json({ message: 'An error occurred.' });
  }
}); 

2. Using Error-Handling Packages

Express.js offers several error-handling middleware packages to streamline error management. One such package is express-error-handler—these packages make it easier to handle and respond to errors by providing ready-to-use functionality, such as custom error messages and error logging features.

To use this package, you need to install it in your project:

 npm install express-error-handler 

Once installed, you can use its features to enhance your application's error-handling capabilities.

 const errorHandler = require('express-error-handler');

// Register the error-handling middleware
app.use(errorHandler({
  static: {
    '404': 'path/to/404.html'
  }
})); 

For instance, in the example above, suppose a user requests a route that doesn't exist. The handler function will trigger and redirect the user to a custom 404 error page, 404.html. This ensures the Express.js application effectively handles a page-not-found error.

Essentially, these packages provide a more user-friendly approach to managing errors that may arise.

3. Handling Synchronous and Asynchronous Errors Using Try-Catch Blocks

Handling synchronous and asynchronous programming errors using try-catch blocks is an effective technique in Express.js. For synchronous code, you can manage errors by wrapping the potentially error-prone section in a try-catch block.

Here's a code sample showcasing try-catch blocks in use:

 app.get('/data', (req, res) => {
  try {
    // code that may cause an error
    const result = someFunction();
    res.json(result);
  } catch (error) {
    console.error('Error occurred:', error);
    res.status(500).json({ message: 'An error occurred.' });
  }
}); 

However, when working with asynchronous operations such as database queries or using Axios to consume APIs, try-catch blocks alone may not be enough. In such cases, you can now integrate the async and await keywords within the blocks to handle errors more efficiently.

Here's some sample code:

 app.get('/data', async (req, res) => {
  try {
    const data = await fetchDataFromDatabase();
    res.json(data);
  } catch (error) {
    console.error('Async Error:', error);
    res.status(500).json({ message: 'Error occurred fetching data.' });
  }
}); 

4. Creating Custom Error-Handling Middleware

Custom error-handling middleware allows you to define how your program handles errors and their corresponding responses, according to your application's requirements.

By creating error-handling middleware functions, you can centralize and customize error management, ensuring a more organized and tailored approach to handling errors across the entire application.

Here is a custom middleware function code example:

 // Custom middleware for handling not found errors
const notFoundHandler = (req, res, next) => {
  const resource = req.params.resource;
  
  if (resource === 'users') {
    return res.status(404).json({ message: 'User not found.' });
  } else if (resource === 'products') {
    return res.status(404).json({ message: 'Product not found.' });
  } else {
    return res.status(404).json({ message: 'Requested resource not found.' });
  }
};

app.use('/api/:resource', notFoundHandler); 

In this example, the notFoundHandler function checks the resource parameter in the request URL. Depending on the value provided, the handler function responds with custom error messages for different types of resources, such as users and products.

For any other resource not explicitly handled, it provides a generic error message. Alternatively, within this middleware, you can also opt to route users to custom error pages which assist them on how to resolve the issues they encountered.

By using this custom error-handling middleware, you can tailor error management and responses to different situations, making error handling more specific and informative.

5. Using Error Logging and Monitoring Tools in Production

In a production environment, it's essential to implement error logging and monitoring to keep track of application errors. Some effective tools you can use include Winston and Morgan, among others. These tools log errors to a file, a centralized server, or a monitoring platform, allowing you to quickly identify and resolve issues.

Here's an example of how you can use Winston in an Express.js application for error logging:

 const winston = require('winston');
const expressWinston = require('express-winston');


app.use(expressWinston.errorLogger({
    // Error logging middleware using Winston
}));
 

Error Management in Backend Applications

Implementing efficient error management techniques and fail-safe procedures is essential in building robust backend applications.

In Express.js applications, it is important to anticipate, plan for and implement effective error-handling techniques that will allow you to quickly identify, manage, and respond to errors. This will guarantee a more reliable and user-friendly experience for your users.