Extensible Custom Error

JavaScript extensible custom error that can take a message and/or an Error object

class MyError extends ExtensibleCustomError {}

new MyError('message'); // Take a message
new MyError(error); // Take an error
new MyError('message', error); // Take a message and an error

Contents

• Features
  • Define custom errors easily
  • Wrap errors without losing any data
• Installation
• Usage
  • Define custom errors
  • Instantiate custom errors
• Examples
  • Wrap an error
  • Wrap an error while passing a new message
• Special Thanks
• License

Features

There are some pains around JavaScript error handling. Two of them are:

1. Define custom errors easily
2. Wrap errors without losing any data

This ExtensibleCustomError class enables you to do both - you can define your custom errors easily and wrap errors with them while merging stack traces prettily.

Define custom errors easily

To define custom errors in Vanilla JS, you need to set names and stack traces manually, but you no longer need to do that with ExtensibleCustomError.

class MyError extends ExtensibleCustomError {}

Wrap errors without losing any data

Built-in errors only take a message, so they can't wrap any errors, which means stack traces so far will be lost. However, ExtensibleCustomError can take a message and/or an Error object while merging stack traces.

catch (error) {
  throw new MyError(error);
}

catch (error) {
  throw new MyError('message', error);
}

Installation

Using npm:

$ npm install extensible-custom-error

Using Yarn:

$ yarn add extensible-custom-error

Usage

Define custom errors

const ExtensibleCustomError = require('extensible-custom-error');

// That's it!
class MyError extends ExtensibleCustomError {}

// Should you need to set custom properties
class MyErrorWithCustomProperty extends ExtensibleCustomError {
  constructor(...args) {
    // Ensure calling the super constructor
    super(...args);

    Object.defineProperty(this, 'customProperty', {
      configurable: true,
      enumerable : false,
      value : 'I am the Bone of my Sword',
      writable : true,
    });
  }
}

N.B. With an uglifier, class names might get obsecure. See this issue comment.

Instantiate custom errors

You can instantiate your custom errors in the same way as built-in errors.

// Throw it as usual!
throw new MyError('Steel is my Body and Fire is my Blood');

try {
  // Do something that may cause errors
} catch (error) {
  // Pass an error instance, then stack traces will be merged
  throw new MyError(error);
}

try {
  // Do something that may cause errors
} catch (error) {
  // Pass a message and an error instance, then stack traces will be merged
  throw new MyError('I have created over a Thousand Blades', error);
}

Examples

Wrap an error

If you run:

const ExtensibleCustomError = require('extensible-custom-error');

class MyError extends ExtensibleCustomError {}

function throwBuiltinError() {
  throw new Error('Unknown to Death, Nor known to Life');
}

function wrapErrorWithMyError() {
  try {
    throwBuiltinError();
  } catch (error) {
    throw new MyError(error);
  }
}

function main() {
  try {
    wrapErrorWithMyError();
  } catch (error) {
    console.log(error);
  }
}

main();

you'll get:

MyError: Error: Unknown to Death, Nor known to Life
    at wrapErrorWithMyError (/home/necojackarc/custom_error.js:101:11)
Error: Unknown to Death, Nor known to Life
    at throwBuiltinError (/home/necojackarc/custom_error.js:94:9)
    at wrapErrorWithMyError (/home/necojackarc/custom_error.js:99:5)
    at main (/home/necojackarc/custom_error.js:107:5)
    at Object.<anonymous> (/home/necojackarc/custom_error.js:113:1)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Function.Module.runMain (module.js:693:10)

Wrap an error while passing a new message

If you run:

const ExtensibleCustomError = require('extensible-custom-error');

class MyError extends ExtensibleCustomError {}

function throwBuiltinError() {
  throw new Error('Have withstood Pain to create many Weapons');
}

function wrapErrorWithMyError() {
  try {
    throwBuiltinError();
  } catch (error) {
    throw new MyError('Unlimited Blade Works', error);
  }
}

function main() {
  try {
    wrapErrorWithMyError();
  } catch (error) {
    console.log(error);
  }
}

main();

you'll get:

MyError: Unlimited Blade Works
    at wrapErrorWithMyError (/home/necojackarc/custom_error.js:101:11)
Error: Have withstood Pain to create many Weapons
    at throwBuiltinError (/home/necojackarc/custom_error.js:94:9)
    at wrapErrorWithMyError (/home/necojackarc/custom_error.js:99:5)
    at main (/home/necojackarc/custom_error.js:107:5)
    at Object.<anonymous> (/home/necojackarc/custom_error.js:113:1)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Function.Module.runMain (module.js:693:10)

Special Thanks

• @yszk0123 as a reviewer
• bjyoungblood/es6-error as a reference

License

The module is available as open source under the terms of the MIT License.