Extending Error Objects in JavaScript

When throwing exceptions in JavaScript, one may desire to extend the built-in Error object to create custom error types. This allows for more specific and informative exception handling.

In JavaScript, Inheritance Isn't Through Subclassing

Unlike in Python, where exceptions are typically subclassed from the Exception base class, JavaScript does not support traditional subclassing for error objects. Instead, it utilizes the concept of prototype extension.

Extending Error Objects in ES6

In ES6, the extends keyword can be used to extend the Error object, creating a custom error constructor:

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

In this example, the MyError class inherits from the Error object and overrides the name property.

Creating Custom Exceptions

To create an instance of the custom error, simply instantiate it like any other object:

throw new MyError('Something went wrong');

Handling Custom Errors

When handling errors, you can use the instanceof operator to check for specific error types:

try {
  // ...
} catch (err) {
  if (err instanceof MyError) {
    // Handle MyError specifically
  } else {
    // Handle other errors
  }
}