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  • License Apache-2.0

Create custom error classes

Package Exports

  • error-custom-class

Readme

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Create custom error classes.

Features

Example

import errorCustomClass from 'error-custom-class'

const UserError = errorCustomClass('UserError')
const DatabaseError = errorCustomClass('DatabaseError')

try {
  throw new UserError('message')
} catch (error) {
  console.log(error.name) // 'UserError'
  console.log(error instanceof UserError) // true
}

Install

npm install error-custom-class

This package is an ES module and must be loaded using an import or import() statement, not require().

API

errorCustomClass(errorName, options?)

errorName string
options Options?
Return value: CustomError

Creates a custom error class.

Options

Options are an optional object with the following members.

onCreate

Type: (error, params) => void

Called on new CustomError('message', params).

const DatabaseError = errorCustomClass('DatabaseError', {
  onCreate(error, { props }) {
    error.dbId = props.databaseId
  },
})
const databaseError = new DatabaseError('message', { props: { databaseId: 2 } })
console.log(databaseError.dbId) // 2
console.log(databaseError.databaseId) // undefined
Error properties

By default, onCreate() sets any params.props as error properties.

const userError = new UserError('message', { props: { userId: 56 } })
console.log(userError.userId) // 56

ParentClass

Type: typeof Error
Default: Error

Parent error class.

const ParentError = errorCustomClass('ParentError')
const ChildError = errorCustomClass('ChildError', { ParentClass: ParentError })
const childError = new ChildError('message')
console.log(childError instanceof ChildError) // true
console.log(childError instanceof ParentError) // true

Best practices

Constructor

A common pattern for custom error classes is:

class CustomError extends Error {
  constructor(message) {
    super(message)
    this.name = 'CustomError'
  }
}

However, this has several issues (which error-custom-class handles):

  • error.cause is not set
  • Unlike native error classes, error.name is:
    • Enumerable, although it should not. For example, for (const key in error) will iterate over name, which is unexpected.
    • Set on the error instance instead of its prototype. In Node.js, this sometimes results in the error name being printed as Error [CustomError] instead of CustomError.

Polyfills

Some Error polyfills (such as es-shims/error-cause) prevent extending from it. This library includes some logic to fix this.

Related projects

Support

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

Everyone is welcome regardless of personal background. We enforce a Code of conduct 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. Pull requests are welcome!