Intermediate JavaScript

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Error Handling in JavaScript

Error handling is an essential part of programming to ensure that our applications behave robustly in unexpected situations. In this chapter, we will explore techniques to efficiently handle errors in JavaScript.

Using `try/catch`

try/catch diagram try/catch diagram

The try/catch block allows capturing errors in the code without interrupting the general flow of the program.

javascript

"In this example, we use 'try/catch' to capture errors in 'riskyFunction'. If the function fails, the error is caught and displayed in the console, preventing the program from stopping."

Throwing Errors with `throw`

We can use throw to generate custom errors when specific conditions occur in our code.

javascript

"Here, we use 'throw' to throw an error if 'age' is less than 18. If the error occurs, it is caught in the 'catch' block and a message is displayed."

`finally` for Additional Executions

The finally block always executes, regardless of whether an error occurs or not. This is useful for freeing resources or performing final tasks.

javascript

"In this case, the 'finally' block executes after attempting to fetch data, regardless of whether the operation was successful or failed."

Error Handling in Asynchronous Functions

In asynchronous functions, errors can be handled with try/catch around await blocks to capture Promise errors.

javascript

"Here, 'try/catch' captures errors in the asynchronous function 'loadUserData' if an issue occurs while fetching the user data."

Error Handling in Promises with `catch`

When working with Promises, catch is essential to handle errors without breaking the execution chain.

javascript

"In this example, we use 'catch' at the end of the Promise chain to capture any error that occurs during the data request."

Custom Errors and Inheritance from `Error`

We can create custom errors by inheriting from the Error class, providing specific messages or additional structures.

javascript

"Here, we create a custom error called 'ValidationError' that throws a specific message if the value is empty. Then we use 'try/catch' to handle this error and display its message."

Error Logging and Monitoring Tools

For production applications, it is essential to log errors and use monitoring tools like Sentry or LogRocket.

javascript

"This code shows an example of how to capture an error in production and send it to a monitoring service, like 'logErrorToService'."

Conclusion

Error handling in JavaScript is fundamental to creating robust applications and avoiding unexpected failures. With the use of try/catch, custom errors, and monitoring tools, you can effectively identify and handle errors.

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