Prototype Chain
Prototype Chain — The prototype chain is JavaScript's mechanism for inheritance, where objects inherit properties and methods from other objects via prototypes. Every JavaScript object has a hidden `[[Prototype]]` property (accessible via `__proto__` or `Object.getPrototypeOf()`) that references another object. When you access a property on an object, JavaScript first checks the object itself, then walks up the prototype chain. This is how inheritance works in JavaScript — classes are syntactic sugar over prototype-based inheritance. This term relates to the Object category of the reference. You will meet prototype chain in practice when working with APIs such as Object.keys(), Object.values(), Object.entries(), Object.assign(). Related terms: Closure, Hoisting, Event Loop, Temporal Dead Zone (TDZ), IIFE (Immediately Invoked Function Expression), Currying. Understanding prototype chain makes the rest of the JavaScript documentation noticeably easier to follow, because the concept recurs across methods, guides, and error messages.