A Complete Guide to Prototypes in JavaScript: How They Work and Why They Matter

What is a Prototype?

Every JavaScript object has an internal link to another object called its prototype, from which it can inherit properties and methods.

Example

function Person(name) {
    this.name = name;
}
Person.prototype.greet = function() {
    return "Hi, I'm " + this.name;
};

let p1 = new Person("Alice");
console.log(p1.greet()); // "Hi, I'm Alice"

Why Prototypes Matter

• They enable prototype-based inheritance, letting objects share methods without duplicating them in memory.
• All arrays, strings, and objects in JavaScript use built-in prototypes for their methods (e.g. Array.prototype.map).
• Understanding prototypes is key to understanding how class syntax works under the hood.