Properly update an error's properties.

Features

• Prevents overriding error core properties (name, message, etc.)
• Protects against prototype pollution
• Prevents overriding existing properties
• Copies another error's properties
• Can set properties as non-enumerable
• Preserves properties descriptors (enumerable, writable, configurable, get/set)
• Exception-safe: this only throws syntax errors
• Strict TypeScript typing of the return value

Example

import setErrorProps from 'set-error-props'

const error = new Error('one')
setErrorProps(error, { prop: true, message: 'two' })
console.log(error.prop) // true
console.log(error.message) // 'one': message is readonly

Install

npm install set-error-props

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

setErrorProps(error, props, options?)

error Error | object
props Error | object
options Options?
Return value: Error

Assigns props to error, then returns error.

Options

soft

Type: boolean
Default: false

Prevents overriding existing properties.

Usage

Error core properties

const error = new Error('one')
setErrorProps(error, { message: 'two' })
console.log(error.message) // 'one'

Prototype pollution

const error = new Error('one')
setErrorProps(error, { toString: () => 'injected' })
console.log(error.toString()) // 'Error: one'
console.log(Error.prototype.toString()) // 'Error'

Overriding protection

const error = new Error('message')
error.one = true
setErrorProps(error, { one: false, two: true }, { soft: true })
console.log(error.one) // true
console.log(error.two) // true

Error copy

const error = new Error('one')
const secondError = new Error('two')
secondError.prop = true
setErrorProps(error, secondError)
console.log(error.message) // 'one'
console.log(error.prop) // true

Non-enumerable properties

const error = new Error('message')

// Properties that start with `_` are not enumerable
setErrorProps(error, { _one: true, two: true })

console.log(error._one) // true
console.log(error.two) // true
console.log(Object.keys(error)) // ['two']
console.log(error) // Prints `two` but not `_one`

Descriptors

const error = new Error('message')
Object.defineProperty(error, 'prop', {
  value: false,
  enumerable: false,
  writable: true,
  configurable: true,
})
setErrorProps(error, { prop: true })
console.log(error.prop) // true
console.log(Object.getOwnPropertyDescriptor(error, 'prop').enumerable) // false

Exception safety

const error = new Proxy(new Error('message'), {
  set() {
    throw new Error('example')
  },
  defineProperty() {
    throw new Error('example')
  },
})
setErrorProps(error, { prop: true }) // This does not throw

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
• normalize-exception: Normalize exceptions/errors
• 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-stack: Properly update an error's stack
• merge-error-cause: Merge an error with its cause
• 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

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!