error-class-utils
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Properly create error classes
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[](https://www.npmjs.com/package/error-class-utils)
[](https://unpkg.com/error-class-utils?module)
[](/src/main.d.ts)
[](https://codecov.io/gh/ehmicky/error-class-utils)
[](https://bundlephobia.com/package/error-class-utils)
[](https://fosstodon.org/@ehmicky)
[](https://medium.com/@ehmicky)
Properly create error classes.
Useful utilities when creating custom error classes.
# Features
- Ponyfill
[`error.cause`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause)
on
[older Node.js and browsers](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause#browser_compatibility)
- Properly [set `error.name`](#seterrornameerrorclass-name)
- Fix [issues](#ensurecorrectclasserror-newtarget) when `Error` has been
polyfilled
# Example
<!-- eslint-disable fp/no-this, fp/no-class, fp/no-mutating-assign -->
```js
import {
ensureCorrectClass,
ponyfillCause,
setErrorName,
} from 'error-class-utils'
export class CustomError extends Error {
constructor(message, parameters) {
super(message, parameters)
// Fix some issues when `Error` has been polyfilled
ensureCorrectClass(this, new.target)
// Ponyfill `error.cause` on old Node.js/browsers
ponyfillCause(this, parameters)
}
}
// Properly set `error.name` as a non-enumerable and inherited property
setErrorName(CustomError, 'CustomError')
```
```js
import { CustomError } from './errors.js'
const cause = new Error('innerMessage')
const error = new CustomError('message', { cause })
console.log(error instanceof CustomError) // true
console.log(error.name) // 'CustomError'
console.log(error.cause) // Error: innerMessage ...
```
# Install
```bash
npm install error-class-utils
```
This package works in both Node.js >=18.18.0 and
[browsers](https://raw.githubusercontent.com/ehmicky/dev-tasks/main/src/browserslist).
This is an ES module. It must be loaded using
[an `import` or `import()` statement](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c),
not `require()`. If TypeScript is used, it must be configured to
[output ES modules](https://www.typescriptlang.org/docs/handbook/esm-node.html),
not CommonJS.
# API
## ensureCorrectClass(error, new.target)
`error` `Error`\
`new.target` `typeof Error`\
_Return value_: `void`
Some `Error` polyfills (such as
[`es-shims/error-cause`](https://github.com/es-shims/error-cause)) prevent
extending from it. This fixes it.
The second argument must be
[`new.target`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new.target).
This must be called directly inside a class constructor, after
[`super(message, parameters)`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/super).
<!-- eslint-disable fp/no-class, fp/no-this -->
```js
import { ensureCorrectClass } from 'error-class-utils'
class CustomError extends Error {
constructor(message, parameters) {
super(message, parameters)
ensureCorrectClass(this, new.target)
}
}
// Thanks to `ensureCorrectClass()`, this is now always true even when
// `Error` has been polyfilled
console.log(new CustomError('message') instanceof CustomError) // true
```
## ponyfillCause(error, parameters?)
`error` `Error`\
`parameters` `ErrorParams?`\
_Return value_: `void`
Ponyfills
[`error.cause`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause)
on
[older Node.js and browsers](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause#browser_compatibility).
This must be called inside a class constructor, after
[`super(message, parameters)`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/super).
<!-- eslint-disable fp/no-class, fp/no-this -->
```js
import { ponyfillCause } from 'error-class-utils'
class CustomError extends Error {
constructor(message, parameters) {
super(message, parameters)
ponyfillCause(this, parameters)
}
}
try {
throw new Error('innerMessage')
} catch (cause) {
// Works on any platforms thanks to ponyfill
const error = new CustomError('message', { cause })
console.log(error.cause.message) // 'innerMessage'
}
```
## setErrorName(ErrorClass, name)
`ErrorClass` `typeof Error`\
`name` `string`\
_Return value_: `void`
Set an `ErrorClass`'s
[`name`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/name).
This must be performed on an error class, not instance. Unlike setting
`this.name = '...'` inside an error's constructor, this follows the native
`Error` classes' pattern where `error.name`:
- Ends with the `Error` suffix
- Matches the
[constructor's `name`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name)
- Is
[inherited](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
- Is
[non-enumerable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
<!-- eslint-disable fp/no-class -->
```js
import { setErrorName } from 'error-class-utils'
class CustomError extends Error {}
setErrorName(CustomError, 'CustomError')
console.log(CustomError.name) // 'CustomError'
console.log(CustomError.prototype.name) // 'CustomError'
const error = new CustomError('message')
console.log(error.name) // 'CustomError'
console.log(Object.keys(error).includes('name')) // false
```
# Related projects
- [`modern-errors`](https://github.com/ehmicky/modern-errors): Handle errors in
a simple, stable, consistent way
- [`error-custom-class`](https://github.com/ehmicky/error-custom-class): Create
one error class
- [`error-serializer`](https://github.com/ehmicky/error-serializer): Convert
errors to/from plain objects
- [`normalize-exception`](https://github.com/ehmicky/normalize-exception):
Normalize exceptions/errors
- [`is-error-instance`](https://github.com/ehmicky/is-error-instance): Check if
a value is an `Error` instance
- [`merge-error-cause`](https://github.com/ehmicky/merge-error-cause): Merge an
error with its `cause`
- [`set-error-class`](https://github.com/ehmicky/set-error-class): Properly
update an error's class
- [`set-error-message`](https://github.com/ehmicky/set-error-message): Properly
update an error's message
- [`wrap-error-message`](https://github.com/ehmicky/wrap-error-message):
Properly wrap an error's message
- [`set-error-props`](https://github.com/ehmicky/set-error-props): Properly
update an error's properties
- [`set-error-stack`](https://github.com/ehmicky/set-error-stack): Properly
update an error's stack
- [`error-cause-polyfill`](https://github.com/ehmicky/error-cause-polyfill):
Polyfill `error.cause`
- [`handle-cli-error`](https://github.com/ehmicky/handle-cli-error): 💣 Error
handler for CLI applications 💥
- [`log-process-errors`](https://github.com/ehmicky/log-process-errors): Show
some ❤ to Node.js process errors
- [`error-http-response`](https://github.com/ehmicky/error-http-response):
Create HTTP error responses
- [`winston-error-format`](https://github.com/ehmicky/winston-error-format): Log
errors with Winston
# Support
For any question, _don't hesitate_ to [submit an issue on GitHub](../../issues).
Everyone is welcome regardless of personal background. We enforce a
[Code of conduct](CODE_OF_CONDUCT.md) in order to promote a positive and
inclusive environment.
# Contributing
This project was made with ❤️. The simplest way to give back is by starring and
sharing it online.
If the documentation is unclear or has a typo, please click on the page's `Edit`
button (pencil icon) and suggest a correction.
If you would like to help us fix a bug or add a new feature, please check our
[guidelines](CONTRIBUTING.md). Pull requests are welcome!
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