// 1. Global context — refers to globalThis (window in browser)
console.log(this); // Window {} in browser

// 2. Regular function — depends on call site
function show() {
  console.log(this);
}
show();            // Window (sloppy) or undefined (strict mode)

// 3. Object method — refers to the object
const user = {
  name: "Alice",
  greet() {
    console.log(`Hi, I'm ${this.name}`);
  }
};
user.greet(); // "Hi, I'm Alice"

// 4. Constructor / class — refers to new instance
class Person {
  constructor(name) {
    this.name = name; // 'this' = the new object
  }
  greet() {
    return `Hello, I'm ${this.name}`;
  }
}
const alice = new Person("Alice");
alice.greet(); // "Hello, I'm Alice"

const timer = {
  count: 0,
  // Regular function — 'this' is lost in callback
  startBroken() {
    setInterval(function() {
      this.count++; // ❌ 'this' is Window, not timer!
    }, 1000);
  },
  // Arrow function — 'this' is inherited from surrounding scope
  start() {
    setInterval(() => {
      this.count++; // ✅ 'this' is timer object
      console.log(this.count);
    }, 1000);
  }
};

function introduce(greeting, punctuation) {
  return `${greeting}, I'm ${this.name}${punctuation}`;
}

const person = { name: "Alice" };

// call() — invoke immediately, args listed separately
introduce.call(person, "Hello", "!");   // "Hello, I'm Alice!"

// apply() — invoke immediately, args as array
introduce.apply(person, ["Hi", "."]); // "Hi, I'm Alice."

// bind() — returns a NEW function with 'this' locked
const aliceIntro = introduce.bind(person);
aliceIntro("Hey", "?"); // "Hey, I'm Alice?"

// Practical bind — fix 'this' in event handlers
class Button {
  constructor(label) {
    this.label = label;
    this.handleClick = this.handleClick.bind(this); // lock 'this'
  }
  handleClick() {
    console.log(`${this.label} clicked`);
  }
}

"use strict";
const learner = {
  name: "Kavi",
  greet() { return "Hi " + this.name; }
};
const boundGreeting = learner.greet.bind(learner);
console.log(learner.greet());
console.log(boundGreeting());