Convert errors to/from plain objects.

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Features

• Ensures errors are safe to serialize with JSON
• Can be used as error.toJSON()
• Deep serialization/parsing, including transforming
• 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 >=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

serialize(errorInstance, options?)

errorInstance any
options Options?
Return value: ErrorObject

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.

const error = new Error('example')
error.inner = new Error('inner')
serialize(error).inner // { name: 'Error', message: 'inner', ... }
serialize(error, { shallow: true }).inner // Error: inner ...

loose

Type: boolean
Default: false

By default, when the argument is not an Error instance, it is converted to one. If this option is true, it is kept as is instead.

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

include

Type: string[]

Only pick specific properties.

serialize(error, { include: ['message'] }) // { message: 'example' }

exclude

Type: string[]

Omit specific properties.

serialize(error, { exclude: ['stack'] }) // { name: 'Error', message: 'example' }

transformObject(errorObject, errorInstance)

Type: (errorObject, errorInstance) => void

Transform each error plain object.

errorObject is the error after serialization. It must be directly mutated.

errorInstance is the error before serialization.

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. They can be inside other errors, plain objects or arrays.

const error = new Error('example')
error.inner = new Error('inner')
const errorObject = serialize(error)

parse(errorObject).inner // Error: inner ...
parse(errorObject, { shallow: true }).inner // { name: 'Error', message: ... }

loose

Type: boolean
Default: false

By default, when the argument is not an error plain object, it is converted to one. If this option is true, it is kept as is instead.

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

transformArgs(constructorArgs, errorObject, ErrorClass)

Type: (constructorArgs, errorObject, ErrorClass) => void

Transform the arguments passed to each new Error().

constructorArgs is the array of arguments. Usually, constructorArgs[0] is the error message and constructorArgs[1] is the constructor options object. constructorArgs must be directly mutated.

errorObject is the error before parsing. ErrorClass is its class.

transformInstance(errorInstance, errorObject)

Type: (errorInstance, errorObject) => void

Transform each Error instance.

errorInstance is the error after parsing. It must be directly mutated.

errorObject is the error before parsing.

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

Omit additional error properties

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

const errorObject = serialize(error, { include: ['name', 'message', 'stack'] })
console.log(errorObject.prop) // undefined
console.log(errorObject) // { name: 'Error', message: 'example', stack: '...' }

Omit stack traces

const error = new Error('example')

const errorObject = serialize(error, { exclude: ['stack'] })
console.log(errorObject.stack) // undefined
console.log(errorObject) // { name: 'Error', message: 'example' }

Deep serialization/parsing

The loose option can be used to deeply serialize/parse objects and arrays.

const error = new Error('example')
const deepArray = serialize([{}, { error }], { loose: true })

const jsonString = JSON.stringify(deepArray)
const newDeepArray = JSON.parse(jsonString)

const newError = parse(newDeepArray, { loose: true })[1].error // Error: example

Transforming

const errors = [new Error('test secret')]
errors[0].date = new Date()

const errorObjects = serialize(errors, {
  loose: true,
  // Serialize `Date` instances as strings
  transformObject: (errorObject) => {
    errorObject.date = errorObject.date.toString()
  },
})
console.log(errorObjects[0].date) // Date string

const newErrors = parse(errorObjects, {
  loose: true,
  // Transform error message
  transformArgs: (constructorArgs) => {
    constructorArgs[0] = constructorArgs[0].replace('secret', '***')
  },
  // Parse date strings as `Date` instances
  transformInstance: (error) => {
    error.date = new Date(error.date)
  },
})
console.log(newErrors[0].message) // 'test ***'
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 in a simple, stable, consistent way
• 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
• 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 💥
• safe-json-value: ⛑️ JSON serialization should never fail
• 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.

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Contributing

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