Custom errors in Javascript are a type of error that can be thrown when code is executed. Custom errors are thrown when code deviates from the expected result or when an unexpected exception is encountered. They can give developers greater control over how errors in Javascript are handled when compared to the default browser and console error messages. This article will dive into what custom errors are, why they are important, how to create and handle them, and the best practices for debugging with them.

What is Custom Error Javascript?

Custom errors are a type of error that is created inside of a Javascript program. Unlike errors reported by a browser or console, custom errors contain extra information that enable developers to track down exactly where an error occurred. Additionally, custom errors enable developers to create more instructive error messages that can be used to appropriately handle unexpected circumstances.

Custom errors are created using the “Error” constructor. This constructor takes two parameters: an error message and the name of the error. Creating an error is typically done using the “throw” command. For example, if you want to create an error with the message “Error: Input must be a string” and the name “InputError”, you can use the following code:

try {    throw new Error("Input must be a string", "InputError");} catch(error) {    console.log(error);} 

When this code is employed, the following output will be returned:

Error: Input must be a string at Object.<anonymous> (test.js:3:21) {     name: "InputError",     message: "Input must be a string" }

The above output indicates that the code created an Error with the name “InputError” and message “Input must be a string”. In addition, the output provides contextual information on where the error was thrown (the line number and file name of the code). This extra context can be extremely helpful during debugging.

Custom errors can also be used to create more user-friendly error messages. For example, instead of displaying a generic error message, a custom error can be used to provide a more descriptive message that explains what went wrong and how to fix it. This can help users understand the issue more quickly and take the appropriate action to resolve it.

Common Types of Custom Errors in Javascript

There are several common types of custom errors that can be thrown in Javascript. These include syntax errors, reference errors, type errors, and range errors. Syntax errors occur when the syntax of a statement is incorrect. Reference errors occur when referencing a non-existent object. Type errors occur when trying to use operations on objects of incompatible data types. Range errors occur when a command is outside of an acceptable range.

Custom errors can also be thrown when a function is called with the wrong number of arguments. This type of error is known as an arity error. Additionally, custom errors can be thrown when a function is called with an argument of the wrong type. This type of error is known as an argument type error. It is important to be aware of these types of errors when writing code in Javascript, as they can cause unexpected behavior.

Understanding the Syntax for Creating Custom Errors

As mentioned above, custom errors are created using the “Error” constructor. This constructor takes two parameters: an error message and the name of the error. In addition, it is important to use the “throw” command to create an Error object and take advantage of contextual information provided by the “catch” statement. For example, if you want to create an Error with the message “Input must be a string” and the name “InputError”, you can use the following code:

try {    throw new Error("Input must be a string", "InputError");} catch(error) {    console.log(error);} 

It is also important to note that custom errors can be used to provide more detailed information about the cause of an error. For example, if an error occurs due to invalid user input, a custom error can be created to provide more information about the type of input that was expected. This can help to make debugging easier and provide more meaningful feedback to the user.

How to Handle Custom Errors in Javascript

When handling custom errors in Javascript, it is important to use the “try…catch” statement in order to capture any exceptions that may be thrown as a result of unexpected input or errors. This statement works by test running a block of code in the “try” statement, and catching any Exceptions thrown by additionally specifying a “catch” statement.

For example, if you want to test run a function that takes an input, you can use a “try…catch” statement like so:

 try {    someFunction(input_value);  } catch(error) {    console.log("An error occurred:" + error);  } 

In the above example, any errors thrown by the function will be caught and printed to the console with a descriptive error message. This enables developers to trap unexpected exceptions and take appropriate action.

It is also important to note that the “try…catch” statement should be used sparingly, as it can slow down the performance of your code. If you are dealing with a large number of exceptions, it may be more efficient to use a different approach such as a switch statement.

Benefits of Using Custom Error Handling

The main benefit of using custom error handling is that it enables developers to have more control over how errors are handled and reported. By creating custom error messages, developers can provide users with more detailed guidance on how to fix errors instead of relying on browser- or console-generated messages. Additionally, custom error handling enables developers to capture and log contextual information that can be used during debugging.

Custom error handling also allows developers to create a more user-friendly experience. By providing users with more detailed information about the error, they can better understand what went wrong and how to fix it. Additionally, custom error handling can help developers identify and address potential issues before they become major problems.

Best Practices for Debugging with Custom Errors

When debugging with custom errors, it is important to remember to use descriptive error messages that are as informative as possible. Additionally, it is important to use appropriate try-catch statements in order to capture any exceptions or errors that may be thrown. Last but not least, it is also important to log contextual information in order to make troubleshooting easier.

Using Third-Party Libraries for Simplified Error Handling

For those looking for simplified error handling with fewer lines of code, it may be worth exploring third-party libraries such as Sentry or LogRocket which provide comprehensive error tracking for Javascript applications in production. These libraries can be easily integrated into existing codebases and enable developers to capture more information on exceptions being thrown by their applications.

Tips for Avoiding Common Mistakes with Custom Errors

When using custom errors, it is important to remember that they should only be used when absolutely necessary, as they can impact performance if used excessively. Additionally, it is important to make sure that all exceptions are caught in order to avoid unexpected behavior. Lastly, always remember to use descriptive error messages and log adequate contextual information.