How to Extend Errors in JavaScript for Custom Error Handling

Extending Errors in JavaScript: A Comprehensive Guide

Error handling is an essential part of any programming language. In JavaScript, Error is the base class for all errors. However, sometimes we may want to create our own custom error types thatinherit from the base Error class but provide additional functionality or properties.

Extending Error Using ES6

With the introduction of ES6, extending Error became much easier. We can now use the extends keyword to create a new class that inherits from Error:

class MyError extends Error {
  constructor(message) {
    super(message);
    this.name = 'MyError';
  }
}

This class extends the Error class and adds a custom name property. We can now throw instances of MyError like this:

throw new MyError('Something went wrong');

When we catch and handle an instance of MyError, we can access its custom name property, which will help us identify the error type:

try {
  // ...
} catch (error) {
  if (error instanceof MyError) {
    console.error(`MyError: ${error.message}`);
  } else {
    console.error(`Unknown error: ${error.message}`);
  }
}

Extending Error Using Legacy JavaScript

In legacy JavaScript, we can extend Error using the prototype chain:

function MyError(message) {
  this.message = message;
}

MyError.prototype = Object.create(Error.prototype);
MyError.prototype.constructor = MyError;
MyError.prototype.name = 'MyError';

This approach is slightly more verbose, but it also works in older versions of JavaScript that don't support ES6.

Conclusion

Extending Error in JavaScript allows us to create custom error types that can be used to provide more detailed information about errors and to handle them specifically. Whether you use ES6 or legacy JavaScript, there is an appropriate way to extend Error to meet your needs.

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