Normalize:

Exceptions that are not Error instances
Error properties (name, message, stack, constructor) that are missing, invalid, enumerable, readonly, non-writable, non-configurable, non-extensible, proxied or throwing
error.cause and error.errors recursively, when present

Example

import normalizeException from 'normalize-exception'

try {
  throw 'message'
} catch (error) {
  console.log(error) // 'message'
  console.log(normalizeException(error)) // Error: message
  console.log(normalizeException(error) instanceof Error) // true
}

Install

npm install normalize-exception

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

normalizeException(error, options?)

error any
options Options
Return value: Error

normalizeException() never throws.

If error is an Error instance, it is returned. Any missing or invalid error property is directly modified.

If it is not an Error instance, a new one is created and returned.

Options

Options are an optional object with the following properties.

shallow

Type: boolean
Default: false

Unless true, error.cause and error.errors are normalized recursively, when present.

Features

Invalid type

Strings

try {
  throw 'message'
} catch (error) {
  console.log(error) // 'message'
  console.log(normalizeException(error)) // Error: message
  console.log(normalizeException(error) instanceof Error) // true
}

Plain objects

try {
  throw { name: 'TypeError', message: 'message' }
} catch (error) {
  console.log(normalizeException(error)) // TypeError: message
}

Others

try {
  throw null
} catch (error) {
  console.log(error.message) // Throws
  console.log(normalizeException(error).message) // 'null'
}

Missing properties

try {
  const error = new TypeError('message')
  error.name = undefined
  throw error
} catch (error) {
  console.log(error.name) // undefined
  console.log(normalizeException(error).name) // 'TypeError'
}

Mismatched constructor

try {
  const error = new TypeError('message')
  error.constructor = RangeError
  throw error
} catch (error) {
  console.log(error.constructor) // RangeError
  console.log(normalizeException(error).constructor) // TypeError
}

Missing stack

try {
  const error = new Error('message')
  error.stack = undefined
  throw error
} catch (error) {
  console.log(error.stack) // undefined
  console.log(normalizeException(error).stack) // 'Error: message ...'
}

Invalid properties

try {
  const error = new Error('message')
  error.message = true
  throw error
} catch (error) {
  console.log(typeof error.message) // 'boolean'
  console.log(typeof normalizeException(error).message) // 'string'
}

Enumerable properties

class ExampleError extends Error {
  constructor(...args) {
    super(...args)
    // Common mistake: this makes `error.name` enumerable
    this.name = 'ExampleError'
  }
}

try {
  throw new ExampleError('message')
} catch (error) {
  console.log({ ...error }) // { name: 'ExampleError' }
  console.log({ ...normalizeException(error) }) // {}
}

Readonly properties

try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', { get: () => 'message' })
  throw error
} catch (error) {
  error.message = 'other' // Throws
  normalizeException(error).message = 'other' // Does not throw
}

Non-writable properties

try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', { value: '', writable: false })
  throw error
} catch (error) {
  error.message = 'other' // Throws
  normalizeException(error).message = 'other' // Does not throw
}

Non-configurable properties

try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', { value: '', configurable: false })
  throw error
} catch (error) {
  delete error.message // Throws
  delete normalizeException(error).message // Does not throw
}

Non-extensible error

try {
  const error = new Error('message')
  Object.preventExtensions(error)
  throw error
} catch (error) {
  error.prop = true // Throws
  normalizeException(error).prop = true // Does not throw
}

Proxies

try {
  throw new Proxy(new Error('message'), {})
} catch (error) {
  const { toString } = Object.prototype
  console.log(toString.call(error)) // '[object Object]'
  console.log(toString.call(normalizeException(error))) // '[object Error]'
}

Throwing properties

Proxies

try {
  throw new Proxy(new Error('message'), {
    get: () => {
      throw new Error('example')
    },
  })
} catch (error) {
  console.log(error.message) // Throws
  console.log(normalizeException(error).message) // Does not throw
}

Getters

try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', {
    get: () => {
      throw new Error('example')
    },
  })
  throw error
} catch (error) {
  console.log(error.message) // Throws
  console.log(normalizeException(error).message) // Does not throw
}

Recursion

`error.cause`

try {
  throw new Error('message', { cause: 'innerError' })
} catch (error) {
  console.log(error.cause instanceof Error) // false
  console.log(normalizeException(error).cause instanceof Error) // true
}

`error.errors`

try {
  throw new AggregateError(['innerError'], 'message')
} catch (error) {
  console.log(error.errors[0] instanceof Error) // false
  console.log(normalizeException(error).errors[0] instanceof Error) // true
}

Related projects

modern-errors: Handle errors in a simple, stable, consistent way
error-custom-class: Create one error class
error-class-utils: Utilities to properly create error classes
error-serializer: Convert errors to/from plain objects
merge-error-cause: Merge an error with its cause
is-error-instance: Check if a value is an Error instance
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 💥
beautiful-error: Prettify error messages and stacks
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.

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!

GeezerVison

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Example

Install

API

normalizeException(error, options?)

Options

shallow

Features

Invalid type

Strings

Plain objects

Others

Missing properties

Mismatched constructor

Missing stack

Invalid properties

Enumerable properties

Readonly properties

Non-writable properties

Non-configurable properties

Non-extensible error

Proxies

Throwing properties

Proxies

Getters

Recursion

error.cause

error.errors

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