Error-class-utils NPM

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