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
• 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', ... }

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. The constructor will be called with a single message argument. It it throws, Error will be used as the error class instead.

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

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

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]

Constructor's arguments

parse() calls new ErrorClass(message, {}) by default. This works well with regular error classes.

When more advanced error classes are used, the constructor's arguments can be explicitly set as an error.constructorArgs property.

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

3.7.0

Features

• Improve tree-shaking support