NodeJS error handling best practices

NodeJS is an open source server-side JavaScript runtime environment based on event-driven, asynchronous I/O. Its efficiency and scalability make NodeJS the technology of choice for many enterprise-level web applications. However, like all other software, NodeJS applications are not completely immune to errors and exceptions. In order to improve the robustness and reliability of your code, it is very important to handle errors correctly.

This article aims to provide some best practices for NodeJS error handling to help developers fundamentally improve the way they handle errors.

1. Using the Error object

JavaScript provides built-in Error objects, which are standard ways to represent runtime errors. In NodeJS, developers can create their own customized error objects based on the Error object to better adapt to the specific needs of the application. The following is a simple example:

class DatabaseConnectionError extends Error {
  constructor(msg, userFriendlyMsg) {
    super(msg);
    this.userFriendlyMsg = userFriendlyMsg;
    this.name = this.constructor.name;
    Error.captureStackTrace(this, this.constructor);
  }
}

In this example, we extend the NodeJS built-in Error object and add a userFriendlyMsg attribute to provide user-friendly error information, and overload the constructor to allow Provide this information transparently while creating the error.

2. Handle asynchronous exceptions gracefully

Since NodeJS is asynchronous I/O, its exception handling method is different from traditional synchronous code. Therefore, handling exceptions in asynchronous code requires following some different rules. Here are two ways to handle asynchronous exceptions gracefully:

1. Exception handling in callback functions

In NodeJS, callback functions are the core of event-driven solutions . Usually, the callback function will take the two-parameter form of (error, data), where the error parameter represents the error that may occur during asynchronous operation, and the data parameter represents the result of the asynchronous operation.

In order to handle exceptions in callback functions gracefully, we recommend using the error-first callback pattern, that is, passing the error object in the first parameter of the callback function. Of course, in some cases, you can use a try-catch statement to catch exceptions in a callback function, but this is generally not a good practice.

The following is a simple example:

function readFile(filePath, callback) {
  fs.readFile(filePath, (err, data) => {
    if (err) {
      callback(new Error(`Failed to read file: ${filePath}`));
    } else {
      callback(null, data);
    }
  });
}

In this example, we manually check for errors in the callback function and pass the error object as the first parameter to the callback.

2. Promise exception handling

Promise is a more elegant way to handle asynchronous code in modern JavaScript. With Promise, exceptions that may occur in asynchronous operations can be handled more naturally. The following is a simple example:

function readFilePromise(filePath) {
  return new Promise((resolve, reject) => {
    fs.readFile(filePath, (err, data) => {
      if (err) {
        reject(new Error(`Failed to read file: ${filePath}`));
      } else {
        resolve(data);
      }
    });
  });
}

In this example, we use the Promise object to handle the operation of asynchronously reading the file, and use the reject method to set the status of the Promise to "rejected" in the event of an exception. . Note that each link in the Promise exception handling chain needs to call the catch method or use the Promise.allSettled() method to ensure that no exceptions are ignored.

3. Write good log records

When an error occurs, logging is an important task. Logs can help us quickly locate problems, find the root cause of errors, and find appropriate solutions.

In NodeJS, logging can use the built-in console object or a third-party logging library, such as winston.js, bunyan, etc.

If you have multiple NodeJS instances or run on multiple servers, you should log errors to a central logging system such as Elasticsearch, Graylog, Logstash, etc.

4. Use appropriate debugging tools

Large server applications like NodeJS can become very complex, and debugging when errors occur can become tricky. To debug NodeJS applications more easily, we can use some appropriate debugging tools. Here are some commonly used debugging tools:

1. Node.js built-in debugger

NodeJS’s built-in debugger is a REPL environment that runs in the NodeJS process. It helps us with interactive debugging at runtime, inspecting variables, executing expressions, stepping through code, and more.

To enable NodeJS's built-in debugger, use the following command line:

node debug [app.js]

2. Chrome Developer Tools

Chrome Developer Tools are web development It is one of the commonly used debugging tools and can also be used to debug NodeJS applications. To debug a NodeJS application using Chrome Developer Tools, use the following command line:

node --inspect[=[host:port]] [app.js]

Then, we can open the Chrome browser and visit the following URL:

chrome://inspect

In "Remote Target ” option, find our NodeJS application and click the “Inspect” button to open the developer tools.

Summary

This article introduces some best practices for NodeJS error handling, which can help developers better manage and resolve errors that occur in web applications. By using Error objects, handling asynchronous exceptions gracefully, writing good logging, and using appropriate debugging tools, we can quickly locate and solve problems, thereby improving the reliability and robustness of our applications.

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