70. Constructor Functions (Legacy OOP)

Before ES6 introduced the class keyword (syntactic sugar), JavaScript used constructor functions to define blueprints for creating multiple objects of the same type.

Defining a Constructor

1. The function is named starting with a capital letter (a convention).
2. It takes parameters to set initial properties.
3. It uses this to assign properties to the newly created object.

javascript function Person(name, age) { this.name = name; this.age = age; this.greet = function() { console.log(Hi, I'm ${this.name}.); }; }

Creating Instances (new Keyword)

To create a new object from this blueprint, we must use the new keyword.

javascript const alice = new Person('Alice', 28); const bob = new Person('Bob', 35);

alice.greet(); // Hi, I'm Alice. console.log(bob.age); // 35

Key: The new keyword automatically creates an empty object, binds this to that object, executes the function, and returns the new object.