class-is

Enhances a JavaScript class by adding an is<Class> property to compare types between realms.

Motivation

Checking if a value is an instance of a class in JavaScript is not an easy task.

You can use instanceof, but that doesn't work between different realms or different versions. Comparing with constructor.name could be a solution but if you need to Uglify the module it doesn't work, as it creates different names for the same module.

So the solution is to use symbols.

Installation

$ npm install class-is

Usage

// Package X
import withIs from 'class-is';

class Person {
    constructor(name, city) {
        this.name = name;
        this.city = city;
    }
}

export default withIs(Person, { className: 'Person', symbolName: '@org/package-x/person' });

// Package Y
import withIs from 'class-is';

class Animal {
    constructor(species) {
        this.species = species;
    }
}

export default withIs(Animal, { className: 'Animal', symbolName: '@org/package-y/animal' });

// Package Z
import Person from 'package-x';
import Animal from 'package-y';

const diogo = new Person('Diogo', 'Porto');
const wolf = new Animal('Gray Wolf');

console.log(Person.isPerson(diogo));
console.log(Person.isPerson(wolf));

Running the example above will print:

true
false

API

withIs(Class, { className: name, symbolName: symbol })

class

Type: class

The class to be enhanced.

className

Type: String

The name of the class your passing.

symbolName

Type: String

Unique id for the class. This should be namespaced so different classes from different modules do not collide and give false positives.

Example: @organization/package/class

Tests

$ npm test
$ npm test -- --watch during development

License

MIT