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    Author message:

    This module was renamed to error-custom-class.

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    3.0.0 • Public • Published

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    Create custom error types.



    Custom error types

    import errorType from 'error-type'
    const UserError = errorType('UserError')
    const DatabaseError = errorType('DatabaseError')
    try {
      throw new UserError('message')
    } catch (error) {
      console.log( // 'UserError'
      console.log(error instanceof UserError) // true

    Error properties

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

    Error cause

    // `error.cause` can be used even in older Node.js or browsers
    try {
    } catch (cause) {
      throw new UserError('message', { cause })

    Custom initialization logic

    const DatabaseError = errorType('DatabaseError', (error, { props }) => {
      error.dbId = props.databaseId
    const databaseError = new DatabaseError('message', { props: { databaseId: 2 } })
    console.log(databaseError.dbId) // 2
    console.log(databaseError.databaseId) // undefined


    npm install error-type

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


    errorType(errorName, onCreate?)

    errorName string
    onCreate (error, params) => void
    Return value: CustomError

    Custom initialization logic

    onCreate(error, params) is optional and is called on new CustomError('message', params).

    By default, it sets any params.props as error properties. However, you can override it with any custom logic to validate, normalize params, etc.

    Best practices


    A common pattern for custom error types is:

    class CustomError extends Error {
      constructor(message) {
        super(message) = 'CustomError'

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

    • error.cause is not set
    • Unlike native error types, 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.


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

    Related projects


    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.


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    npm i error-type

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    • ehmicky