EnumerationValue

EnumerationValue (from scenerystack/phet-core) is the base class every value of a closed, PhET-style enumeration extends — see the Enumeration Pattern for the full "why" and a worked example. This page documents EnumerationValue itself: what it provides once its sibling class Enumeration has scanned a subclass's static instances and wired them up.

import { EnumerationValue, Enumeration } from 'scenerystack/phet-core';

Usage

class Direction extends EnumerationValue {
  public static readonly NORTH = new Direction();
  public static readonly SOUTH = new Direction();

  // Must come last: scans the static instances declared above.
  public static readonly enumeration = new Enumeration( Direction );
}

Direction.NORTH.name;              // 'NORTH' - filled in by the Enumeration constructor
Direction.NORTH.enumeration.values; // [ Direction.NORTH, Direction.SOUTH ]
Direction.NORTH.toString();        // 'NORTH'

Before new Enumeration( Direction ) runs, a freshly-constructed EnumerationValue's name and enumeration are unset — reading them throws. Enumeration's constructor walks Object.keys on the class (and its supertypes, to support augmenting an existing enumeration) looking for instanceof matches, and assigns name/enumeration on each one it finds, in declaration order.

Members

Member	Description
name (getter)	The static property key the instance was assigned to (e.g. 'NORTH'); throws if read before Enumeration has run
enumeration (getter)	The owning Enumeration<this> instance; throws if read before Enumeration has run
toString()	Returns name
EnumerationValue.sealedCache	A Set of constructors that already have an Enumeration built for them — Enumeration's constructor adds to it, and the base EnumerationValue constructor throws if you try to new a sealed constructor directly (subclassing it further is still fine)

name and enumeration are set-once: assigning either a second time throws, which is what makes them safe to treat as immutable identity after construction.

You cannot construct new values after Enumeration has run

Calling new Enumeration( Direction ) seals Direction in EnumerationValue.sealedCache — any subsequent new Direction() throws. Declare every static instance before the public static readonly enumeration = new Enumeration( Direction ) line, and add that line last, exactly once, per concrete enumeration class.