Normalize-exception NPM

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

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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
}