Extensible Custom Error

!CI

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

``js
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

- Extensible Custom 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.

$3

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.

`js
class MyError extends ExtensibleCustomError {}
`

$3

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.

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

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

Installation

Using npm:

`bash
$ npm install extensible-custom-error
`

Usage

$3

`js
// CommonJS
const ExtensibleCustomError = require('extensible-custom-error');
// ESM
// import ExtensibleCustomError from 'extensible-custom-error';

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

`js
// 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.

$3

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

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

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

`js
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

$3

If you run:

`js
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:

`bash
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. (/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)
`

$3

If you run:

`js
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:

`bash
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. (/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.