https://github.com/es-shims/error.iserror
An ESnext spec-compliant `Error.isError` shim/polyfill/replacement that works as far down as ES3.
https://github.com/es-shims/error.iserror
ecmascript error iserror javascript polyfill shim
Last synced: 4 months ago
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An ESnext spec-compliant `Error.isError` shim/polyfill/replacement that works as far down as ES3.
- Host: GitHub
- URL: https://github.com/es-shims/error.iserror
- Owner: es-shims
- License: mit
- Created: 2024-10-15T18:23:43.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2025-07-24T21:56:46.000Z (6 months ago)
- Last Synced: 2025-09-28T04:44:39.303Z (4 months ago)
- Topics: ecmascript, error, iserror, javascript, polyfill, shim
- Language: JavaScript
- Homepage:
- Size: 36.1 KB
- Stars: 2
- Watchers: 3
- Forks: 2
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Funding: .github/FUNDING.yml
- License: LICENSE
Awesome Lists containing this project
README
# Error.isError [![Version Badge][npm-version-svg]][package-url]
[![github actions][actions-image]][actions-url]
[![coverage][codecov-image]][codecov-url]
[![License][license-image]][license-url]
[![Downloads][downloads-image]][downloads-url]
[![npm badge][npm-badge-png]][package-url]
An ESnext spec-compliant `Error.isError` shim/polyfill/replacement that works as far down as ES3.
This package implements the [es-shim API](https://github.com/es-shims/api) interface. It works in an ES3-supported environment and complies with the proposed [spec](https://tc39.es/proposal-is-error/).
## Getting started
```sh
npm install --save error.iserror
```
## Usage/Examples
```js
const isError = require('error.iserror');
var assert = require('assert');
assert.equal(isError(undefined), false);
assert.equal(isError(null), false);
assert.equal(isError({}), false);
assert.equal(isError([]), false);
assert.equal(isError(Error), false);
assert.equal(isError({ __proto__: Error.prototype, constructor: Error }), false);
assert.equal(isError(new Error()), true);
assert.equal(isError(new EvalError()), true);
assert.equal(isError(new RangeError()), true);
assert.equal(isError(new ReferenceError()), true);
assert.equal(isError(new SyntaxError()), true);
assert.equal(isError(new TypeError()), true);
assert.equal(isError(new URIError()), true);
if (typeof AggregateError === 'function') {
assert.equal(isError(new AggregateError([])), true);
}
if (typeof SuppressedError === 'function') {
assert.equal(isError(new SuppressedError()), true);
}
// note: engines that have `Symbol.toStringTag`, and lack structuredClone, and lack other brand-checking
// mechanisms, are only capable of brand-checking Error objects when they lack a `Symbol.toStringTag` property in their
// prototype chain. An object with it will give the wrong answer.
// This affects node 6 - 9, Chrome 49 - 97, Safari 10 - 14, Edge 15 - 18
assert.equal(isError({ __proto__: Error.prototype, constructor: Error, [Symbol.toStringTag]: 'Error' }), false);
const err = Object.assign(new Error(), { [Symbol.toStringTag]: 'Non-Error' });
Object.setPrototypeOf(err, null);
assert.equal(isError(err), true);
// note: node < v24.3 has an `Error.isError` that does not work correctly with DOMException objects
assert.equal(isError(new DOMException()), true);
```
```js
var shimIsError = require('error.iserror/shim');
const getPolyfill = require('error.iserror/polyfill');
var assert = require('assert');
/* when Error.isError is not present */
delete Error.isError;
var shimmed = shimIsError();
assert.equal(shimmed, getPolyfill());
assert.deepEqual(Error.isError(new Error()), isError(new Error()));
```
```js
var shimIsError = require('error.iserror/shim');
var assert = require('assert');
/* when Error.isError is present */
var shimmed = shimIsError();
assert.equal(shimmed, Error.isError);
assert.deepEqual(Error.isError(new Error()), isError(new Error()));
```
## Tests
Simply clone the repo, `npm install`, and run `npm test`
[package-url]: https://npmjs.org/package/error.iserror
[npm-version-svg]: https://versionbadg.es/es-shims/Error.isError.svg
[deps-svg]: https://david-dm.org/es-shims/Error.isError.svg
[deps-url]: https://david-dm.org/es-shims/Error.isError
[dev-deps-svg]: https://david-dm.org/es-shims/Error.isError/dev-status.svg
[dev-deps-url]: https://david-dm.org/es-shims/Error.isError#info=devDependencies
[npm-badge-png]: https://nodei.co/npm/error.iserror.png?downloads=true&stars=true
[license-image]: https://img.shields.io/npm/l/error.iserror.svg
[license-url]: LICENSE
[downloads-image]: https://img.shields.io/npm/dm/error.iserror.svg
[downloads-url]: https://npm-stat.com/charts.html?package=error.iserror
[codecov-image]: https://codecov.io/gh/es-shims/Error.isError/branch/main/graphs/badge.svg
[codecov-url]: https://app.codecov.io/gh/es-shims/Error.isError/
[actions-image]: https://img.shields.io/endpoint?url=https://github-actions-badge-u3jn4tfpocch.runkit.sh/es-shims/Error.isError
[actions-url]: https://github.com/es-shims/Error.isError/actions