Properly create error classes.

Useful utilities when creating custom error classes.

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Features

• Ponyfill error.cause on older Node.js and browsers
• Properly set error.name
• Fix issues when Error has been polyfilled

Example

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')

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

npm install error-class-utils

This package works in both Node.js >=18.18.0 and browsers.

This is an ES module. It must be loaded using an import or import() statement, not require(). If TypeScript is used, it must be configured to output ES modules, 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) prevent extending from it. This fixes it.

The second argument must be new.target. This must be called directly inside a class constructor, after super(message, parameters).

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 on older Node.js and browsers.

This must be called inside a class constructor, after super(message, parameters).

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.

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
• Is inherited
• Is non-enumerable

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: Handle errors in a simple, stable, consistent way
• error-custom-class: Create one error class
• error-serializer: Convert errors to/from plain objects
• normalize-exception: Normalize exceptions/errors
• is-error-instance: Check if a value is an Error instance
• merge-error-cause: Merge an error with its cause
• set-error-class: Properly update an error's class
• set-error-message: Properly update an error's message
• wrap-error-message: Properly wrap an error's message
• set-error-props: Properly update an error's properties
• set-error-stack: Properly update an error's stack
• error-cause-polyfill: Polyfill error.cause
• handle-cli-error: 💣 Error handler for CLI applications 💥
• log-process-errors: Show some ❤ to Node.js process errors
• error-http-response: Create HTTP error responses
• winston-error-format: Log errors with Winston

Support

For any question, don't hesitate to submit an issue on GitHub.

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Contributing

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