12. Method Borrowing: call(), apply(), bind() & Custom Polyfills • JavaScript & Advanced ES6+ (0-to-Hero Big Tech Standard) • Rishabh Ki Kaksha

Soch tere dost ke paas ek sports car (Function) hai, par tere paas car nahi hai. Tu dost se bolta hai: *"Bhai 1 ghante ke liye apni car de de, drive mai karunga (tera context lagg jayega)."*

JavaScript me kisi doosre object ke function ko **apne object ke data ke sath run karne ko Method Borrowing kehte hain.**  
Aur ye kaam 3 methods karte hain: **`call()`**, **`apply()`**, **`bind()`**.

**Tagline yaad rakh:**
> `call()` = Call now with Comma-separated arguments  
> `apply()` = Apply now with Array of arguments  
> `bind()` = Baad me call karne ke liye Bind karke naya function le lo

---

### 2. `call()`, `apply()`, `bind()` Deep Dive

```javascript
const doctor = {
    specialty: "Cardiologist",
    introduce: function(greeting, hospital) {
        return `${greeting}! I am a ${this.specialty} at ${hospital}.`;
    }
};

const engineer = {
    specialty: "AI Systems Architect"
};

// 1. call(): Turant execute karega, arguments comma se alag honge
console.log(doctor.introduce.call(engineer, "Hello", "Google AI Lab"));
// Output: "Hello! I am a AI Systems Architect at Google AI Lab."

// 2. apply(): Turant execute karega, arguments ARRAY me honge
console.log(doctor.introduce.apply(engineer, ["Hey", "DeepMind"]));
// Output: "Hey! I am a AI Systems Architect at DeepMind."

// 3. bind(): Turant execute NAHI karega, ek NAYA permanently bound function return karega
const engineerIntro = doctor.introduce.bind(engineer, "Namaste");
console.log(engineerIntro("Antigravity Systems"));
// Output: "Namaste! I am a AI Systems Architect at Antigravity Systems."
```

---

### 3. Master Comparison Matrix

---

### 4. Big Tech Interview Polyfill: `myBind` From Scratch

Top Big Tech interviews (Google, Meta, Amazon) me `Function.prototype.bind` ka polyfill scratch se likhne ko pucha jata hai:

```javascript
Function.prototype.myBind = function(context, ...boundArgs) {
    // 1. Check karo ki caller function hi hai
    if (typeof this !== 'function') {
        throw new TypeError('myBind can only be called on functions');
    }

const originalFunction = this; // 'this' yahan wo original function hai jise bind kiya ja raha hai

return function(...callArgs) {
        // 2. Bound arguments aur runtime arguments ko merge karo
        const allArgs = [...boundArgs, ...callArgs];
        // 3. Original function ko target context ke sath execute karo
        return originalFunction.apply(context, allArgs);
    };
};

// Verification
function getDetails(city, country) {
    return `${this.name} lives in ${city}, ${country}`;
}

const user = { name: "Rishabh" };
const customBound = getDetails.myBind(user, "Jaipur");
console.log(customBound("India")); 
// Output: "Rishabh lives in Jaipur, India" ✅
```

---

### 5. `call()` Aur `apply()` Ke Top Real-World Hacks

```javascript
// Hack 1: Array ke Max/Min nikalna bina loop ke
const scores = [45, 99, 12, 88, 105];
const maxScore = Math.max.apply(null, scores); // 105

// Hack 2: Array-like object (arguments ya NodeList) ko pure Array me badalna
function listArguments() {
    const argsArray = Array.prototype.slice.call(arguments);
    return argsArray.map(x => x * 10);
}
```

---

### 6. Interview Ke 3 Sawal Is Topic Se

1. **`call` aur `apply` me kya difference hai?** -> Sirf argument passing ka difference hai: `call` me comma-separated arguments aate hain, `apply` me single array aata hai.
2. **`bind` kiye huye function ko dubara `bind` kar sakte hain?** -> Nahi! Ek baar bind hone ke baad dubara bind karne par bhi context pehle wale se hi locked rehta hai.
3. **Arrow function par `call/apply/bind` lagane se kya hota hai?** -> Koi asar nahi hota! Arrow function ka `this` lexically fixed hota hai aur use override nahi kiya ja sakta.

---
**Next Topic:** 13. Event Loop Masterclass: Call Stack, Web APIs, Microtasks & Macrotasks

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PHP 8+ & Laravel 11 Master Track