https://github.com/cfware/instanceof-unifier

Allow `instanceof` to match even if comparing an instance created by a different copy of the class
https://github.com/cfware/instanceof-unifier

Last synced: 29 days ago
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Allow `instanceof` to match even if comparing an instance created by a different copy of the class

• Host: GitHub
• URL: https://github.com/cfware/instanceof-unifier
• Owner: cfware
• License: mit
• Created: 2019-10-22T03:44:25.000Z (about 5 years ago)
• Default Branch: master
• Last Pushed: 2019-10-22T15:57:34.000Z (about 5 years ago)
• Last Synced: 2024-04-26T10:21:47.973Z (8 months ago)
• Language: JavaScript
• Size: 6.84 KB
• Stars: 0
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# instanceof-unifier

[![Travis CI][travis-image]][travis-url]

[![NPM Version][npm-image]][npm-url]

[![NPM Downloads][downloads-image]][downloads-url]

[![MIT][license-image]](LICENSE)

Allow `instanceof` to match even if comparing an instance created by a different

copy of the class.  This module requires node.js 6.5.0 or above to function.

## instanceofUnifier(Class, matcher)

Calling this function makes alterations to the way `instanceof` works on `Class`.

`matcher` must be a `string`.

The user is responsible for picking a unique matcher name.  It is recommended to use

`@:package-local-id`.  Version does not have to match the package

version but it is important to increment it any time a version update is not compatible

with previous versions.

## Example Usage

Create an ESM module:

```js

// index.mjs

import instanceofUnifier from 'instanceof-unifier';

export class MyClass {

}

instanceofUnifier(MyClass, '[email protected]:MyClass');

```

Transpile to Commonjs (babel output shown):

```js

// index.cjs

"use strict";

Object.defineProperty(exports, "__esModule", {

  value: true

});

exports.MyClass = void 0;

var _instanceofUnifier = _interopRequireDefault(require("instanceof-unifier"));

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

class MyClass {}

exports.MyClass = MyClass;

(0, _instanceofUnifier.default)(MyClass, '[email protected]:MyClass');

```

This avoids the divergent specifier hazard for `instanceof`.  You can test:

```js

import indexCJS from './index.cjs';

import {MyClass as ESM} from './index.mjs';

const CJS = indexCJS.MyClass;

const cjs = new CJS();

const esm = new ESM();

if (cjs instanceof CJS && cjs instanceof ESM) {

	console.log('cjs is instanceof both classes');

}

if (esm instanceof CJS && esm instanceof ESM) {

	console.log('esm is instanceof both classes');

}

```

In addition to the divergent specifier hazard this also ensures `instanceof` matches

between multiple copies of your module.

[npm-image]: https://img.shields.io/npm/v/instanceof-unifier.svg

[npm-url]: https://npmjs.org/package/instanceof-unifier

[travis-image]: https://travis-ci.org/cfware/instanceof-unifier.svg?branch=master

[travis-url]: https://travis-ci.org/cfware/instanceof-unifier

[downloads-image]: https://img.shields.io/npm/dm/instanceof-unifier.svg

[downloads-url]: https://npmjs.org/package/instanceof-unifier

[license-image]: https://img.shields.io/npm/l/instanceof-unifier.svg