@northscaler/better-enum

Better enumeration support for TypeScript than its `enum` keyword. This class is modeled after [Java's enumeration pattern](https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html), where enums are instances of classes. This library provides a base

Usage no npm install needed!

<script type="module">
  import northscalerBetterEnum from 'https://cdn.skypack.dev/@northscaler/better-enum';
</script>

README

better-enum

Better enumeration support for TypeScript than its enum keyword. This class is modeled after Java's enumeration pattern, where enums are instances of classes. This library provides a base Enumeration class, along with some conventions and patterns specific to the notion of enumerated values.

TL;DR

Here's a very simple "Hello, World!" enumeration.

import { _of, _values, Enumeration } from '@northscaler/better-enum' // 1️⃣ 

export default class HelloWorld extends Enumeration<HelloWorld> {    // 2️⃣
  static readonly HELLO = new HelloWorld('HELLO', 0)                 // 3️⃣
  static readonly WORLD = new HelloWorld('WORLD', 1)

  static of(it: HelloWorld | string | number): HelloWorld {          // 4️⃣
    return _of(it, HelloWorld)
  }

  static values(): HelloWorld[] {                                    // 5️⃣
    return _values<HellowWorld>(HelloWorld)
  }

  private constructor(name: string, ordinal: number) {               // 6️⃣
    super(name, ordinal, HelloWorld)
  }
}

1️⃣ Import Northscaler's enumeration support

2️⃣ Define your enum to extend Enumeration

3️⃣ Define your enum instances with their name & ordinal (additional, arbitrary properties are allowed, too)

4️⃣ Define a static of() method that converts from string names and number ordinals to the enum instance

5️⃣ Define a static values() method that returns all values of this enum type

6️⃣ Define a private constructor that takes the name & ordinal for an enum instance (again, additional properties are allowed, too)

Now use it.

// mocha test examples

expect(HelloWorld.of('HELLO')).to.equal(HelloWorld.HELLO)          // 1️⃣
expect(HelloWorld.of('WORLD')).to.equal(HelloWorld.WORLD)

expect(HelloWorld.of(0)).to.equal(HelloWorld.HELLO)                // 2️⃣
expect(HelloWorld.of(1)).to.equal(HelloWorld.WORLD)

expect(`${HelloWorld.WORLD}`).to.equal('WORLD')                    // 3️⃣

expect(HelloWorld.WORLD.toFullyQualifiedString()).to.equal(        // 4️⃣
  'HelloWorld:WORLD:1'
)
expect(() => HelloWorld.of('')).to.throw(                          // 5️⃣
  UnidentifiableEnumerationValueError
)
expect(() => HelloWorld.of(-42)).to.throw(
  UnidentifiableEnumerationValueError
)

1️⃣ Convert from an enum's name to its instance

2️⃣ Convert from an enum's ordinal to its instance

3️⃣ Default string form of an enum is its name

4️⃣ Fully qualified string includes colon-separated type, name & ordinal

5️⃣ UnidentifiableEnumerationValueError thrown on argument that can't be converted to an enum instance

NOTE: There are helpful IDE-specific templates to assist you in following the patterns prescribed by this library. See ./src/templates for more information. If you don't see templates for your IDE, please submit a pull/merge request.

Features

name() instance method

This is an instance method that returns the instances name.

ordinal() instance method

This is an instance method that returns the instance's ordinal.

toJSON() instance method

This is an instance method to return the enum as an object suitable for JSON stringification. It simply returns the name of this instance.

static values() method

This is a static method on your enumeration class that returns all instances of the class.

static of() method

This is a static method on your enumeration class that returns an instance of the class given its name or ordinal.

Convenient sorting functions

This package exports two convenient sorting functions, sortByName & sortByOrdinal to sort enumeration instances by their name or ordinal, respectively.

Arbitrary additional properties & methods

Your enumeration class can define any additional properties or methods that you'd like.

Here's an example of a tri-state boolean (true, false or neither) with additional property definite and toBoolean(). It also demonstrates the use of an incrementing ordinal to assign the ordinal values.

import { _of, _values, Enumeration } from '@northscaler/better-enum'

let ordinal = -1 // convenient way to assign ordinals below

/**
 * A tristate boolean.
 */
export default class Bool extends Enumeration<Bool> {
  static readonly NEITHER = new Bool('NEITHER', ordinal++, false)
  static readonly FALSE = new Bool('FALSE', ordinal++, true)
  static readonly TRUE = new Bool('TRUE', ordinal++, true)

  static of(it: Bool | string | number): Bool {
    return _of(it, Bool)
  }

  static values(): Bool[] {
    return _values<Bool>(Bool)
  }

  private constructor(
    _name: string,
    _ordinal: number,
    private _definite: boolean
  ) {
    super(_name, _ordinal, Bool)
  }

  /**
   * Returns `true` of this enum is {@link Bool.TRUE} or {@link Bool.FALSE}.
   * If this enum is {@link Bool.NEITHER}, returns `false`.
   */
  get definite() {
    return this._definite
  }

  /**
   * Converts this {@link Bool} to a `boolean` if it's definite, else throws an `Error`.
   */
  toBoolean() {
    if (this === Bool.TRUE) return true
    if (this === Bool.FALSE) return false
    throw new Error('neither true nor false')
  }
}

Now, you can use your arbitrary properties:

// mocha test examples

expect(Bool.TRUE.definite).to.be.true
expect(Bool.FALSE.definite).to.be.true
expect(Bool.NEITHER.definite).to.be.false

Java's Planet enum

We ported Java's Planet enum example at https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html to this library. It makes significant use of custom properties & methods.

See the enum class and its test if you're curious.