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 💥
• 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

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