JavaScript Tutorial: Prototypes
The prototype chain, Object.create, how classes work under the hood, and property lookup in JavaScript.
The engine under the classes
ES6 classes are syntax sugar over JavaScript's prototype system. Understanding prototypes explains everything about how JavaScript works — why methods are shared, how inheritance actually functions, and why `instanceof` works.
This is what separates JavaScript developers who know the language from those who just use it.
What you'll learn in this JavaScript prototypes tutorial
This interactive JavaScript tutorial has 8 hands-on exercises. Estimated time: 20 minutes.
- Every object has a prototype — Every JavaScript object has a hidden link to another object — its **prototype**. When you access a property that doesn't…
- The prototype chain lookup — When you access `obj.property`, JavaScript looks:
- Classes are prototype sugar — ES6 class syntax compiles down to prototype-based code. The class version and the prototype version are identical under …
- Object.create — manual prototype chain — `Object.create(proto)` creates a new object with `proto` as its prototype — without a constructor function.
- hasOwnProperty vs in — Two ways to check if a property exists:
- Extending built-in prototypes — why NOT to — You CAN add methods to built-in prototypes — but you almost never should:
- Object.assign vs spread — `Object.assign(target, ...sources)` copies properties from sources to target.
- Build a prototype-based inheritance chain — Final challenge — using the prototype approach (no classes).
JavaScript Prototypes concepts covered
- The engine under the classes