This example demonstrates a JavaScript Enum implementation that combines ES6 classes, type checking, and immutability through Object.freeze. It shows how EnumSymbol instances store symbolic identifiers alongside optional numeric values and descriptions, while the Enum class provides collection methods like symbols(), keys(), and contains(). The code includes concrete usage examples with BackoffStrategy and ReadyState enums, illustrating value comparison, display formatting, and description access. It relies on ES6 Symbol.for, computed properties, and the assert library for validation.