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JavaScript classes are syntactic sugar for prototype-based inheritance. Understanding the chain is essential for debugging real-world code.

Under the hood:

• rex.__proto__ === Dog.prototype
• Dog.prototype.__proto__ === Animal.prototype
• Animal.prototype.__proto__ === Object.prototype
• Object.prototype.__proto__ === null

When rex.speak() is called, JS walks the chain until it finds speak.

Inspect the chain:

Direct manipulation (avoid in production code, but useful to know):

Plain objects' prototype chain:

Object.create(null) — true blank object with no prototype, no toString, no hasOwnProperty. Useful for hashmap-like usage:

Class fields and methods are added to the prototype (methods) or the instance (fields):

Performance: lookups walk the chain — deep chains slow down hot code. Most code: don't worry. JIT-compiled hot paths: keep chains shallow.