error-serializer

Convert errors to/from plain objects.

Features

• Ensures errors are safe to serialize with JSON
• Can be used as error.toJSON()
• Deep serialization/parsing, including event callbacks
• Custom serialization/parsing (e.g. YAML or process.send())
• Keeps both native (TypeError, etc.) and custom error classes
• Preserves errors' additional properties
• Can keep constructor's arguments
• Works recursively with error.cause and AggregateError
• Normalizes invalid errors
• Safe: this never throws

Example

import { serialize, parse } from 'error-serializer'

const error = new TypeError('example')
const errorObject = serialize(error)
// Plain object: { name: 'TypeError', message: 'example', stack: '...' }

const errorString = JSON.stringify(errorObject)
const newErrorObject = JSON.parse(errorString)

const newError = parse(newErrorObject)
// Error instance: 'TypeError: example ...'

Install

npm install error-serializer

This package works in both Node.js >=14.18.0 and browsers. It is an ES module and must be loaded using an import or import() statement, not require().

API

serialize(errorInstance, options?)

errorInstance any
options Options?
Return value: object

Convert an Error instance into a plain object.

Options

Object with the following optional properties.

shallow

Type: boolean
Default: false

Unless this option is true, nested errors are also serialized. They can be inside other errors, plain objects or arrays.

serialize([{ error: new Error('test') }]) // [{ error: { name: 'Error', ... } }]
serialize([{ error: new Error('test') }], { shallow: true }) // [{ error: Error }]

normalize

Type: boolean
Default: false

Convert errorInstance to an Error instance if it is not one.

serialize('example') // 'example'
serialize('example', { normalize: true }) // { name: 'Error', message: 'example', ... }

beforeSerialize(errorInstance)

Type: (errorInstance) => void

Called before serializing each errorInstance.

afterSerialize(errorInstance)

Type: (errorInstance) => void

Called after serializing each errorInstance.

parse(errorObject, options?)

errorObject any
options Options?
Return value: Error

Convert an error plain object into an Error instance.

Options

Object with the following optional properties.

classes

Type: object

Custom error classes to keep when parsing.

• Each key is an errorObject.name
• Each value is the error class to use

const errorObject = serialize(new CustomError('example'))
// `CustomError` class is kept
const error = parse(errorObject, { classes: { CustomError } })
// Map `CustomError` to another class
const otherError = parse(errorObject, { classes: { CustomError: TypeError } })

shallow

Type: boolean
Default: false

Unless this option is true, nested error plain objects are also parsed.

const errorObject = serialize(new Error('test'))

parse([{ error: errorObject }])
// [{ error: Error }]
parse([{ error: errorObject }], { shallow: true })
// [{ error: { name: 'Error', ... } }]

normalize

Type: boolean
Default: false

Convert errorObject to an error plain object if it is not one.

parse('example') // 'example'
parse('example', { normalize: true }) // Error: example

beforeParse(errorObject)

Type: (errorObject) => void

Called before parsing each errorObject.

afterParse(errorObject)

Type: (errorObject) => void

Called after parsing each errorObject.

Usage

JSON safety

Error plain objects are always safe to serialize with JSON.

const error = new Error('example')
error.cycle = error

// Cycles make `JSON.stringify()` throw, so they are removed
serialize(error).cycle // undefined

error.toJSON()

serialize() can be used as error.toJSON().

class CustomError extends Error {
  /* constructor(...) { ... } */

  toJSON() {
    return serialize(this)
  }
}
const error = new CustomError('example')

error.toJSON()
// { name: 'CustomError', message: 'example', stack: '...' }
JSON.stringify(error)
// '{"name":"CustomError","message":"example","stack":"..."}'

Custom serialization/parsing

Errors are converted to/from plain objects, not strings. This allows any serialization/parsing logic to be performed.

import { dump, load } from 'js-yaml'

const error = new Error('example')
const errorObject = serialize(error)
const errorYamlString = dump(errorObject)
// name: Error
// message: example
// stack: Error: example ...
const newErrorObject = load(errorYamlString)
const newError = parse(newErrorObject) // Error: example

Additional error properties

const error = new TypeError('example')
error.prop = true

const errorObject = serialize(error)
console.log(errorObject.prop) // true
const newError = parse(errorObject)
console.log(newError.prop) // true

Events

const error = new Error('test')
error.date = new Date()
const errors = [error]

const errorObjects = serialize(errors, {
  // Serialize `Date` instances as strings
  beforeSerialize(errorArg) {
    errorArg.date = errorArg.date.toString()
  },
  // Restore `error.date` after serializing it
  afterSerialize(errorArg) {
    errorArg.date = new Date(errorArg.date)
  },
})
console.log(errorObjects[0].date) // Date string

const newErrors = parse(errorObjects, {
  // Parse date strings as `Date` instances
  beforeParse(errorObjectArg) {
    errorObjectArg.date = new Date(errorObjectArg.date)
  },
  // Restore `errorObject.date` after parsing
  afterParse(errorObjectArg) {
    errorObjectArg.date = errorObjectArg.date.toString()
  },
})
console.log(newErrors[0].date) // `Date` instance

error.cause and AggregateError

const innerErrors = [new Error('one'), new Error('two')]
const cause = new Error('three')
const error = new AggregateError(innerErrors, 'four', { cause })

const errorObject = serialize(error)
// {
//   name: 'AggregateError',
//   message: 'four',
//   stack: '...',
//   cause: { name: 'Error', message: 'three', stack: '...' },
//   errors: [{ name: 'Error', message: 'one', stack: '...' }, ...],
// }
const newError = parse(errorObject)
// AggregateError: four
//   [cause]: Error: three
//   [errors]: [Error: one, Error: two]

Constructors

By default, when an error with custom classes is parsed, its constructor is not called. In most cases, this is not a problem since any property previously set by that constructor is still preserved, providing it is serializable and enumerable.

However, the error.constructorArgs property can be set to call the constructor with those arguments. It it throws, Error will be used as a fallback error class.

class CustomError extends Error {
  constructor(prefix, message) {
    super(`${prefix} - ${message}`)
    this.constructorArgs = [prefix, message]
  }
}
CustomError.prototype.name = 'CustomError'

const error = new CustomError('Prefix', 'example')

const errorObject = serialize(error)
// This calls `new CustomError('Prefix', 'example')`
const newError = parse(errorObject, { classes: { CustomError } })

Related projects

• modern-errors: Handle errors like it's 2022 🔮
• modern-errors-serialize: Serialize/parse errors
• error-custom-class: Create one error class
• error-class-utils: Utilities to properly create error classes
• normalize-exception: Normalize exceptions/errors
• is-error-instance: Check if a value is an Error instance
• merge-error-cause: Merge an error with its cause
• set-error-class: Properly update an error's class
• set-error-message: Properly update an error's message
• set-error-props: Properly update an error's properties
• error-cause-polyfill: Polyfill error.cause
• handle-cli-error: 💣 Error handler for CLI applications 💥
• safe-json-value: ⛑️ JSON serialization should never fail
• log-process-errors: Show some ❤ to Node.js process errors

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!

ehmicky 💻 🎨 🤔 📖

Pedro Augusto de Paula Barbosa 🐛 📖

Changelog

4.0.0

Breaking changes

• When parsing an error and the classes option was defined, the constructor is not called anymore unless error.constructorArgs was set

Features

• Added options beforeSerialize(), afterSerialize(), beforeParse() and afterParse() to customize the serialization and parsing of each error