14_instanceof_operator.js

// `instanceof` Operator

// What
// - The instanceof operator checks if an object is an instance of a specific constructor. In simpler terms, it verifies if an object was created using a particular constructor function.

// Why
// - Type Checking: It helps ensure objects are of the expected type, especially in object-oriented programming. This can prevent errors that might arise when using objects of the wrong type.
// - Conditional Logic: We can use instanceof in conditional statements to perform actions based on the object's type. For example, checking if an object is a Person before accessing its name property.
// - Inheritance Verification: In object-oriented programming with inheritance, you can use instanceof to verify if an object inherits from a specific base class.

// How
// - The instanceof operator works by examining the object's prototype chain. Every object in JavaScript has a prototype, which is another object used as a blueprint for properties and methods. The instanceof operator checks if the constructor function's prototype appears anywhere in the object's prototype chain.

// Syntax
// object instanceof constructor

// Example
function Person(name, age) {
  this.name = name;
  this.age = age;
}

let person1 = new Person("Alice", 30);
console.log(person1 instanceof Person); // Output: true (person1 is an instance of Person)

let num = 10;
console.log(num instanceof Person); // Output: false (num is not an instance of Person)

// Note
// - instanceof only checks the constructor function used to create the object, not the object's actual type (which is always "object" in JavaScript).
// - Modifying the prototype chain after object creation can affect the result of instanceof.