Normalize:

- Exceptions that are not Error instances
- Error properties (name, message, stack, constructor) that are
missing, invalid,
enumerable, readonly,
non-writable,
non-configurable,
non-extensible, proxied or
throwing
- error.cause
and
error.errors
recursively, when present

Example

``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.

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

normalizeException(error, options?)

error any\
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.

$3

Options are an optional object with the following properties.

#### shallow

_Type_: boolean\
_Default_: false

Unless true,
error.cause
and
error.errors
are normalized recursively, when present.

Features

Invalid type

$3

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

$3

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

$3

`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

`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

`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

`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

`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

`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

`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

`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

$3

`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
}
`

$3

`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

$3

`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
}
`

$3

`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: 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
- merge-error-cause: Merge an
error with its cause
- 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-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 💥
- 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

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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!