JavaScript Constructor Functions: Creating Multiple Object Instances

// 🏭 A constructor function — note the Capital name (convention!)function Student(name, age) {  this.name = name;              // "this" = the new object being built  this.age = age;}
// 🍪 Manufacturing instances with new:const s1 = new Student("Priya", 22);const s2 = new Student("Amit", 24);const s3 = new Student("Riya", 21);
console.log(s1.name);
// "Priya"console.log(s2.age);    // 24console.log(s3.name);   // "Riya" — three independent objects from one blueprint ✅

const s1 = new Student("Priya", 22);

① 🆕 A brand-new empty object is created: {
}② 🔗 The object is linked to Student's prototype   (more on prototypes in a moment!)
③ 🎯 The constructor runs with `this` = that new object:   this.name = "Priya"   →   { name: "Priya" }   this.age  = 22        →   { name: "Priya", age: 22 }
④ 📤 The finished object is automatically returned   (unless you explicitly return a different object — rare!)

function Student(name) {
  this.name = name;
  console.log("constructor ran! this =", this);
  // watch step ③ happen}
  const s1 = new Student("Priya");
  // "constructor ran! this = Student { name: 'Priya' }" ✅
  console.log(s1 instanceof Student);
  // true — the prototype link from step ② ✅

function Student(name) {
  this.name = name;
}const s = Student("Priya");
// 😱 no "new"!
console.log(s);
// undefined — nothing was returned!console.log(window.name);        // "Priya" 💀 — leaked onto the GLOBAL object!

// ⚠️ The wasteful way:function Student(name) {  this.name = name;  this.greet = function() {              // defined INSIDE the constructor    return `Hi, I'm ${this.name} 👋`;  };}
const s1 = new Student("Priya");
const s2 = new Student("Amit");
console.log(s1.greet === s2.greet);
// false 😱 — two SEPARATE copies!

function Student(name) {
  this.name = name;
  // ✅ data per instance}
  // ✅ methods go on the PROTOTYPE — shared by ALL instances:Student.prototype.greet = function() {  return `Hi, I'm ${this.name} 👋`;};
  const s1 = new Student("Priya");
  const s2 = new Student("Amit");
  console.log(s1.greet());
  // "Hi, I'm Priya 👋"console.log(s2.greet());              // "Hi, I'm Amit 👋"console.log(s1.greet === s2.greet);   // true ✅ — ONE shared copy!

// 🏭 Constructor function style (pre-2015):
function Student(name) {
  this.name = name;
}Student.prototype.greet = function() {
  return `Hi, I'm ${this.name}`;
};
// 🏛️ Class style (2015+) — same machinery, cleaner wrapping:
class Student {
  constructor(name) {
    this.name = name;
  } greet() {
    return `Hi, I'm ${this.name}`;
  }
}

class Student {
}console.log(typeof Student);
// "function" 😮 — classes are functions underneath!

function Student(name) {
  this.name = name;
}function Teacher(name) {
  this.name = name;
}const s1 = new Student("Priya");
console.log(s1 instanceof Student);
// true ✅
console.log(s1 instanceof Teacher);
// false
console.log(s1 instanceof Object);
// true — everything descends from Object!

new Array(1, 2, 3);
// [1, 2, 3]  (literal [] is the shortcut)
new Object();
// {}         (literal {} is the shortcut)
new Date();
// today's date (Lesson 33!)
new Promise((res, rej) => {
});
// Lesson 26!
new Map();
// a Map

// ⚔️ Character factory — constructor + prototype (pre-class style)
function Character(name, health) {
  this.name = name;
  this.health = health;
}// Shared methods on the prototype — ONE copy for all characters:
Character.prototype.attack = function(target) {
  target.health -= 10;
  console.log(`⚔️ ${this.name} hits ${target.name}! (${target.name}: ${target.health} HP)`);
};
Character.prototype.isAlive = function() {
  return this.health > 0;
};
// 🍪 Manufacture the fighters:
const hero = new Character("Arjun", 100);
const villain = new Character("Duryodhan", 80);
hero.attack(villain);
// ⚔️ Arjun hits Duryodhan! (70 HP)
villain.attack(hero);
// ⚔️ Duryodhan hits Arjun! (90 HP)
hero.attack(villain);
// ⚔️ 60 HP
console.log(hero.isAlive());
// true
console.log(hero.attack === villain.attack);
// true — ONE shared method ✅
console.log(hero instanceof Character);
// true ✅