Properly update an error's properties.

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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 >=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

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!

ehmicky/set-error-props