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Creating Custom Errors in JavaScript

Creating Custom Errors in JavaScript

JavaScript provides a set of 8 error objects that are raised in a try/catch expression based on the type of error encountered. These error objects are:

  • Error
  • EvalError
  • RangeError
  • ReferenceError
  • SyntaxError
  • TypeError
  • URIError

If you want to create your own custom errors in JavaScript, you can extend the base Error class. This allows you to handle different error types in a specific way, without relying solely on error messages to determine the type of error.

To create a custom error, you can define a new class that extends the Error class. Here’s an example:

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class OutOfFuelError extends Error {}

class FlatTireError extends Error {}

Once you have defined your custom error classes, you can handle them in a try/catch block by checking the instance of the error. Here’s an example:

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try {
  // some code
} catch (err) {
  if (err instanceof OutOfFuelError) {
    // handle OutOfFuelError
  } else if (err instanceof FlatTireError) {
    // handle FlatTireError
  }
}

Note that before you can handle a custom error, you need to explicitly throw the error in your code. For example:

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try {
  const car = new Car(); // imagine we have a Car object

  if (!car.fuel) {
    throw new OutOfFuelError('No fuel!');
  }
  if (car.flatTire) {
    throw new FlatTireError('Flat tire!');
  }
} catch (err) {
  if (err instanceof OutOfFuelError) {
    // handle OutOfFuelError
  } else if (err instanceof FlatTireError) {
    // handle FlatTireError
  }
}

When creating a custom error, you can also customize aspects of the class, including the parameters received by the constructor if needed. Here’s an example:

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class OutOfFuelError extends Error {
  constructor(message) {
    super(message);
    this.name = "OutOfFuelError";
  } 
}

In conclusion, creating custom errors in JavaScript allows you to handle different error types in a more specific and controlled manner. By extending the base Error class, you can define your own error classes and handle them accordingly in your code.

tags: [“JavaScript”, “custom errors”, “error handling”]