Prototype Basics in JavaScript
From the JavaScript cheat sheet · Prototypes & Inheritance · verified Jul 2026
Prototype Basics
Understanding the prototype chain
javascript
// Every object has a prototype
const obj = {};
obj.__proto__; // Object.prototype
// Constructor prototype
function Person(name) {
this.name = name;
}
Person.prototype.greet = function() {
return `Hello, I'm ${this.name}`;
};
const john = new Person('John');
john.greet(); // method from prototype💡 Prototype chain: object -> prototype -> prototype -> null
⚡ Methods on prototype are shared, properties usually on instance
📌 Use Object.getPrototypeOf() instead of __proto__
🔥 instanceof checks entire prototype chain