Some utilities around JavaScript Error creation and manipulation.

• written in TypeScript
• no dependencies

Usage

Exposed constants: known error fields

Exposes the properties we can expect on a JavaScript "Error" object.

See the source code for more details.

import {
	STRICT_STANDARD_ERROR_FIELDS,
	QUASI_STANDARD_ERROR_FIELDS,
	COMMON_ERROR_FIELDS,
	COMMON_ERROR_FIELDS_EXTENDED,
} from '@offirmo/error-utils'

Note that COMMON_ERROR_FIELDS_EXTENDED contains private properties, but since they are optional and have rare names, there shouldn't be any conflict.

Exposed types: error interface with more properties

• XError (eXtended error) = with properties up to COMMON_ERROR_FIELDS
• XXError = idem with properties up to COMMON_ERROR_FIELDS_EXTENDED

import {
	XError,
	XXError,
} from '@offirmo/error-utils'

Utility: slightly more convenient way to create errors than new Error(…)

Allows passing additional properties along the error creation, in one go.

• if the properties are recognized as top level (COMMON_ERROR_FIELDS_EXTENDED) they'll be attached directly
• if not, they'll be attached to a root details property

Also:

• Will ensure that the string "error" is present in the message (case-insensitive), will prepend it if not
• Will pick the message from the details as a fallback if the 1st param is not provided/falsy (convenience for rare cases)

import { createError } from '@offirmo/error-utils'

// classic = it's the same
const err = new Error(`Foo API: bar is incorrect!`)
const err = createError(`Foo API: bar is incorrect!`) // return type = XXError

// advanced: extra properties
const err = createError(`Foo API: bar is incorrect!`, { statusCode: 401, foo: 'bar' })

// advanced: extra properties + custom constructor
const err = createError(`Foo API: bar is incorrect!`, { statusCode: 401, foo: 'bar' }, TypeError)
// above is equivalent to:
const err = new TypeError(`Foo API: bar is incorrect!`)
err.statusCode = 401
err.details = {
	foo: 'bar',
}

Utility: normalize anything into a true, writable Error object

Normalize anything into a true, normal error.

Anything can be thrown in JavaScript: undefined, string, number... But that's obviously not a good practice. Even Error-like objects are sometime fancy:

• seen: in a browser, sometimes, an error-like, un-writable object is thrown
• seen: frozen
• seen: non-enumerable props

So we want to ensure a true, safe, writable error object.

NOTE: will always recreate the error

import { normalizeError } from '@offirmo/error-utils'

try {
	...(unreliable code)
}
catch (err_like) {
	throw normalizeError(err_like)
}

See also

• https://github.com/jshttp/http-errors