# normalize-exception

> Normalize exceptions/errors

Latest version **4.0.1** (published 2025-03-29) · MIT license · 0 weekly downloads

## Install

```sh
npm install normalize-exception
pnpm add normalize-exception
yarn add normalize-exception
bun add normalize-exception
```

## Health

**Score 55/100 (C)** — status: stable.

Positive: has types; esm support; no vulnerabilities; high maintenance score; high quality score.

Warnings: low downloads.

Negative: stale.

## Facts

| | |
|---|---|
| Version | 4.0.1 |
| Published | 2025-03-29 |
| First published | 2022-06-09 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Node | >=18.18.0 |
| Dependencies | 2 |
| Unpacked size | 24.6 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 15 |
| Author | ehmicky |
| Maintainers | ehmicky |
| Keywords | nodejs, javascript, stacktrace, library, typescript, browser, errors, monitoring, error-monitoring, message, error-handler, properties, error-handling, error, code-quality, cause, error-reporting, error-classes, normalization, exceptions |

## Links

- npm: https://www.npmjs.com/package/normalize-exception
- Repository: https://github.com/ehmicky/normalize-exception
- Homepage: https://www.github.com/ehmicky/normalize-exception
- Issues: https://github.com/ehmicky/normalize-exception/issues
- npm.io page: https://npm.io/package/normalize-exception

## Dependencies (2)

- [is-plain-obj](https://npm.io/package/is-plain-obj.md) ^4.1.0
- [is-error-instance](https://npm.io/package/is-error-instance.md) ^3.0.1

## Alternatives

- [@sentry/react-native](https://npm.io/package/@sentry/react-native.md) — 2.6M weekly downloads
- [@ardatan/aggregate-error](https://npm.io/package/@ardatan/aggregate-error.md) — 708.1K weekly downloads
- [custom-error-generator](https://npm.io/package/custom-error-generator.md) — 2.0K weekly downloads
- [@technik-sde/prosemirror-recreate-transform](https://npm.io/package/@technik-sde/prosemirror-recreate-transform.md) — 1.5K weekly downloads
- [@suchipi/error-utils](https://npm.io/package/@suchipi/error-utils.md) — 78 weekly downloads

## Recent versions

- 4.0.1 (latest) — 2025-03-29
- 4.0.0 — 2023-10-28
- 3.0.0 — 2023-05-13
- 2.11.0 — 2022-11-11
- 2.10.0 — 2022-11-07
- 2.9.0 — 2022-10-23
- 2.8.1 — 2022-10-13
- 2.8.0 — 2022-10-13
- 2.7.0 — 2022-10-13
- 2.6.0 — 2022-10-06
- 2.5.2 — 2022-10-01
- 2.5.1 — 2022-08-29
- 2.5.0 — 2022-08-29
- 2.4.0 — 2022-08-28
- 2.3.2 — 2022-08-28
- … 24 more at https://npm.io/package/normalize-exception/versions

## README

[![Node](https://img.shields.io/badge/-Node.js-808080?logo=node.js&colorA=404040&logoColor=66cc33)](https://www.npmjs.com/package/normalize-exception)
[![Browsers](https://img.shields.io/badge/-Browsers-808080?logo=firefox&colorA=404040)](https://unpkg.com/normalize-exception?module)
[![TypeScript](https://img.shields.io/badge/-Typed-808080?logo=typescript&colorA=404040&logoColor=0096ff)](/src/main.d.ts)
[![Codecov](https://img.shields.io/badge/-Tested%20100%25-808080?logo=codecov&colorA=404040)](https://codecov.io/gh/ehmicky/normalize-exception)
[![Minified size](https://img.shields.io/bundlephobia/minzip/normalize-exception?label&colorA=404040&colorB=808080&logo=webpack)](https://bundlephobia.com/package/normalize-exception)
[![Mastodon](https://img.shields.io/badge/-Mastodon-808080.svg?logo=mastodon&colorA=404040&logoColor=9590F9)](https://fosstodon.org/@ehmicky)
[![Medium](https://img.shields.io/badge/-Medium-808080.svg?logo=medium&colorA=404040)](https://medium.com/@ehmicky)

Normalize:

- Exceptions that are [not `Error` instances](#invalid-type)
- Error properties (`name`, `message`, `stack`, `constructor`) that are
  [missing](#missing-properties), [invalid](#invalid-properties),
  [enumerable](#enumerable-properties), [readonly](#readonly-properties),
  [non-writable](#non-writable-properties),
  [non-configurable](#non-configurable-properties),
  [non-extensible](#non-extensible-error), [proxied](#proxies) or
  [throwing](#throwing-properties)
- [`error.cause`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause)
  and
  [`error.errors`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
  [recursively](#recursion), when present

# Example

<!-- eslint-disable no-throw-literal -->

```js
import normalizeException from 'normalize-exception'

try {
  throw 'message'
} catch (error) {
  console.log(error) // 'message'
  console.log(normalizeException(error)) // Error: message
  console.log(normalizeException(error) instanceof Error) // true
}
```

# Install

```bash
npm install normalize-exception
```

This package works in both Node.js >=18.18.0 and
[browsers](https://raw.githubusercontent.com/ehmicky/dev-tasks/main/src/browserslist).

This is an ES module. It must be loaded using
[an `import` or `import()` statement](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c),
not `require()`. If TypeScript is used, it must be configured to
[output ES modules](https://www.typescriptlang.org/docs/handbook/esm-node.html),
not CommonJS.

# API

## normalizeException(error, options?)

`error` `any`\
`options` [`Options`](#options)\
_Return value_: `Error`

`normalizeException()` never throws.

If `error` is an `Error` instance, it is returned. Any missing or invalid error
property is directly modified.

If it is not an `Error` instance, a new one is created and returned.

### Options

Options are an optional object with the following properties.

#### shallow

_Type_: `boolean`\
_Default_: `false`

Unless `true`,
[`error.cause`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause)
and
[`error.errors`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
are normalized [recursively](#recursion), when present.

# Features

## Invalid type

### Strings

<!-- eslint-disable no-throw-literal -->

```js
try {
  throw 'message'
} catch (error) {
  console.log(error) // 'message'
  console.log(normalizeException(error)) // Error: message
  console.log(normalizeException(error) instanceof Error) // true
}
```

### Plain objects

<!-- eslint-disable no-throw-literal -->

```js
try {
  throw { name: 'TypeError', message: 'message' }
} catch (error) {
  console.log(normalizeException(error)) // TypeError: message
}
```

### Others

<!-- eslint-disable unicorn/no-null, no-throw-literal -->

```js
try {
  throw null
} catch (error) {
  console.log(error.message) // Throws
  console.log(normalizeException(error).message) // 'null'
}
```

## Missing properties

```js
try {
  const error = new TypeError('message')
  error.name = undefined
  throw error
} catch (error) {
  console.log(error.name) // undefined
  console.log(normalizeException(error).name) // 'TypeError'
}
```

## Mismatched constructor

<!-- eslint-disable fp/no-delete -->

```js
try {
  const error = new TypeError('message')
  error.constructor = RangeError
  throw error
} catch (error) {
  console.log(error.constructor) // RangeError
  console.log(normalizeException(error).constructor) // TypeError
}
```

## Missing stack

```js
try {
  const error = new Error('message')
  error.stack = undefined
  throw error
} catch (error) {
  console.log(error.stack) // undefined
  console.log(normalizeException(error).stack) // 'Error: message ...'
}
```

## Invalid properties

```js
try {
  const error = new Error('message')
  error.message = true
  throw error
} catch (error) {
  console.log(typeof error.message) // 'boolean'
  console.log(typeof normalizeException(error).message) // 'string'
}
```

## Enumerable properties

<!-- eslint-disable fp/no-class, fp/no-this, fp/no-mutation -->

```js
class ExampleError extends Error {
  constructor(...args) {
    super(...args)
    // Common mistake: this makes `error.name` enumerable
    this.name = 'ExampleError'
  }
}

try {
  throw new ExampleError('message')
} catch (error) {
  console.log({ ...error }) // { name: 'ExampleError' }
  console.log({ ...normalizeException(error) }) // {}
}
```

## Readonly properties

<!-- eslint-disable fp/no-mutating-methods, fp/no-get-set, fp/no-mutation -->

```js
try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', { get: () => 'message' })
  throw error
} catch (error) {
  error.message = 'other' // Throws
  normalizeException(error).message = 'other' // Does not throw
}
```

## Non-writable properties

<!-- eslint-disable fp/no-mutating-methods, fp/no-mutation -->

```js
try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', { value: '', writable: false })
  throw error
} catch (error) {
  error.message = 'other' // Throws
  normalizeException(error).message = 'other' // Does not throw
}
```

## Non-configurable properties

<!-- eslint-disable fp/no-mutating-methods, fp/no-delete -->

```js
try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', { value: '', configurable: false })
  throw error
} catch (error) {
  delete error.message // Throws
  delete normalizeException(error).message // Does not throw
}
```

## Non-extensible error

<!-- eslint-disable fp/no-mutation -->

```js
try {
  const error = new Error('message')
  Object.preventExtensions(error)
  throw error
} catch (error) {
  error.prop = true // Throws
  normalizeException(error).prop = true // Does not throw
}
```

## Proxies

<!-- eslint-disable fp/no-proxy, no-shadow -->

```js
try {
  throw new Proxy(new Error('message'), {})
} catch (error) {
  const { toString } = Object.prototype
  console.log(toString.call(error)) // '[object Object]'
  console.log(toString.call(normalizeException(error))) // '[object Error]'
}
```

## Throwing properties

### Proxies

<!-- eslint-disable fp/no-proxy, no-shadow -->

```js
try {
  throw new Proxy(new Error('message'), {
    get: () => {
      throw new Error('example')
    },
  })
} catch (error) {
  console.log(error.message) // Throws
  console.log(normalizeException(error).message) // Does not throw
}
```

### Getters

<!-- eslint-disable fp/no-mutating-methods, fp/no-get-set -->

```js
try {
  const error = new Error('message')
  Object.defineProperty(error, 'message', {
    get: () => {
      throw new Error('example')
    },
  })
  throw error
} catch (error) {
  console.log(error.message) // Throws
  console.log(normalizeException(error).message) // Does not throw
}
```

## Recursion

### `error.cause`

```js
try {
  throw new Error('message', { cause: 'innerError' })
} catch (error) {
  console.log(error.cause instanceof Error) // false
  console.log(normalizeException(error).cause instanceof Error) // true
}
```

### `error.errors`

```js
try {
  throw new AggregateError(['innerError'], 'message')
} catch (error) {
  console.log(error.errors[0] instanceof Error) // false
  console.log(normalizeException(error).errors[0] instanceof Error) // true
}
```

# Related projects

- [`modern-errors`](https://github.com/ehmicky/modern-errors): Handle errors in
  a simple, stable, consistent way
- [`error-custom-class`](https://github.com/ehmicky/error-custom-class): Create
  one error class
- [`error-class-utils`](https://github.com/ehmicky/error-class-utils): Utilities
  to properly create error classes
- [`error-serializer`](https://github.com/ehmicky/error-serializer): Convert
  errors to/from plain objects
- [`merge-error-cause`](https://github.com/ehmicky/merge-error-cause): Merge an
  error with its `cause`
- [`is-error-instance`](https://github.com/ehmicky/is-error-instance): Check if
  a value is an `Error` instance
- [`set-error-class`](https://github.com/ehmicky/set-error-class): Properly
  update an error's class
- [`set-error-message`](https://github.com/ehmicky/set-error-message): Properly
  update an error's message
- [`wrap-error-message`](https://github.com/ehmicky/wrap-error-message):
  Properly wrap an error's message
- [`set-error-props`](https://github.com/ehmicky/set-error-props): Properly
  update an error's properties
- [`set-error-stack`](https://github.com/ehmicky/set-error-stack): Properly
  update an error's stack
- [`error-cause-polyfill`](https://github.com/ehmicky/error-cause-polyfill):
  Polyfill `error.cause`
- [`handle-cli-error`](https://github.com/ehmicky/handle-cli-error): 💣 Error
  handler for CLI applications 💥
- [`log-process-errors`](https://github.com/ehmicky/log-process-errors): Show
  some ❤ to Node.js process errors
- [`error-http-response`](https://github.com/ehmicky/error-http-response):
  Create HTTP error responses
- [`winston-error-format`](https://github.com/ehmicky/winston-error-format): Log
  errors with Winston

# Support

For any question, _don't hesitate_ to [submit an issue on GitHub](../../issues).

Everyone is welcome regardless of personal background. We enforce a
[Code of conduct](CODE_OF_CONDUCT.md) 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](CONTRIBUTING.md). Pull requests are welcome!

<!-- Thanks go to our wonderful contributors: -->

<!-- ALL-CONTRIBUTORS-LIST:START -->
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---
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