serialize-error

Serialize/deserialize an error into a plain object

Useful if you for example need to JSON.stringify() or process.send() the error.

Install

npm install serialize-error

Usage

import {serializeError, deserializeError} from 'serialize-error';

const error = new Error('🦄');

console.log(error);
//=> [Error: 🦄]

const serialized = serializeError(error);

console.log(serialized);
//=> {name: 'Error', message: '🦄', stack: 'Error: 🦄\n    at Object.<anonymous> …'}

const deserialized = deserializeError(serialized);

console.log(deserialized);
//=> [Error: 🦄]

Error constructors

When a serialized error with a known name is encountered, it will be deserialized using the corresponding error constructor, while unknown error names will be deserialized as regular errors:

import {deserializeError} from 'serialize-error';

const known = deserializeError({
	name: 'TypeError',
	message: '🦄'
});

console.log(known);
//=> [TypeError: 🦄] <-- Still a TypeError

const unknown = deserializeError({
	name: 'TooManyCooksError',
	message: '🦄'
});

console.log(unknown);
//=> [Error: 🦄] <-- Just a regular Error

The list of known errors can be extended globally. This also works if serialize-error is a sub-dependency that's not used directly, as long as the project ends up with a single physical copy of the package. Registrations live in that copy's module state, so a duplicate, which is easy to end up with through version skew or a nested install, keeps its own separate list and does not see them.

import {addKnownErrorConstructor} from 'serialize-error';
import {MyCustomError} from './errors.js'

addKnownErrorConstructor(MyCustomError);

For error constructors that require arguments, you can provide a factory function:

import {addKnownErrorConstructor} from 'serialize-error';

class CustomError extends Error {
	name = 'CustomError';

	constructor(message, options) {
		super(message);
		this.code = options.code;
	}
}

addKnownErrorConstructor(CustomError, () => new CustomError('', {code: 'ERR_UNICORN'}));

The constructor, or the factory if given, must return an extensible Error instance, since the payload's properties are added to it.

API

serializeError(value, options?)

Serialize an Error object into a plain object.

• Custom properties are preserved.
• All properties are made enumerable (name, message, stack, cause, errors), so the result survives JSON.stringify().
• Primitive values (including null, undefined, strings, numbers, etc.) and functions are wrapped in a NonError error and serialized.
• Buffer properties are replaced with [object Buffer].
• Stream properties are replaced with [object Stream].
• Circular references are handled.
• If the input object has a .toJSON() method, then it's called instead of serializing the object's properties.
• A .toJSON() that returns the object it received is ignored, since that would hand back the original rather than a copy.
• It's up to .toJSON() implementation to handle circular references and enumerability of the properties.

value

Type: Error | unknown

toJSON implementation examples

import {serializeError} from 'serialize-error';

class ErrorWithDate extends Error {
	constructor() {
		super();
		this.date = new Date(0);
	}
}

const error = new ErrorWithDate();

console.log(serializeError(error));
//=> {name, message, stack, date: '1970-01-01T00:00:00.000Z'}

import {serializeError} from 'serialize-error';

const error = new Error('Unicorn');

error.horn = {
	toJSON() {
		return 'x';
	}
};

serializeError(error);
// => {name, message, stack, horn: 'x'}

deserializeError(value, options?)

Deserialize a plain object or any value into an Error object.

• Error objects are passed through.
• Objects with a string message property are interpreted as errors. Arrays never are, even with a message property.
• All other values are wrapped in a NonError error.
• Custom properties are preserved.
• Non-enumerable properties are kept non-enumerable (name, message, stack, cause, errors).
• Enumerable properties are kept enumerable (all properties besides the non-enumerable ones).
• Circular references are handled.
• Native error constructors are preserved (TypeError, DOMException, etc) and more can be added.

value

Type: {message: string} | unknown

options

Type: object

maxDepth

Type: number
Default: Number.POSITIVE_INFINITY

The maximum depth of properties to preserve when serializing/deserializing.

import {serializeError} from 'serialize-error';

const error = new Error('🦄');
error.one = {two: {three: {}}};

console.log(serializeError(error, {maxDepth: 1}));
//=> {name: 'Error', message: '🦄', stack: 'Error: 🦄\n    at Object.<anonymous> …', one: {}}

console.log(serializeError(error, {maxDepth: 2}));
//=> {name: 'Error', message: '🦄', stack: 'Error: 🦄\n    at Object.<anonymous> …', one: { two: {} }}

useToJSON

Type: boolean
Default: true

Indicate whether to use a .toJSON() method if encountered in the object. This is useful when a custom error implements its own serialization logic via .toJSON() but you prefer to not use it.

isErrorLike(value)

Predicate to determine whether a value looks like an error, even if it's not an instance of Error. It must be an object with string name, message, and stack properties.

import {isErrorLike} from 'serialize-error';

const error = new Error('🦄');
error.one = {two: {three: {}}};

isErrorLike({
	name: 'DOMException',
	message: 'It happened',
	stack: 'at foo (index.js:2:9)',
});
//=> true

isErrorLike(new Error('🦄'));
//=> true

isErrorLike(serializeError(new Error('🦄')));
//=> true

isErrorLike({
	name: 'Bluberricious pancakes',
	stack: 12,
	ingredients: 'Blueberry',
});
//=> false

Limitations

• Deep nesting can overflow the call stack. Set maxDepth to limit recursion.
• Map, Set, RegExp, ArrayBuffer, and DataView serialize as empty objects.
• toJSON() results are returned as-is and may be primitives. They must handle their own circular references and BigInts. useToJSON only applies to serialization.
• Getters and registered constructors/factories can throw. Registered constructors/factories must consistently return extensible errors.
• Nested objects with both pipe() and on() methods are treated as streams.
• DOMException usually deserializes as a plain Error because its name differs from its constructor name.
• Serialization may reorder properties, including those of nested plain objects.
• Deserialized errors have non-enumerable error properties. Call serializeError() before passing them to JSON.stringify().