Example with Function: user.getName?.();

The function is called only if getName exists and is callable.

Common Use: Very useful when working with API responses where some properties may be missing.

37. What is nullish coalescing (??)

The nullish coalescing operator returns the right-hand value when the left-hand value is null or undefined.

Example:

const username = null;
console.log(username ?? "Guest");

Output: Guest

Important Difference From ||

|| considers all falsy values: console.log(0 || 100); → 100

?? only checks null and undefined: console.log(0 ?? 100); → 0

Interview Tip: Use ?? when 0, false, or "" are valid values that should not be replaced.

38. What are object methods?

An object method is a function stored as a property of an object.

Example:

const user = {
    name: "Deepak",
    greet() {
        console.log(`Hello ${this.name}`);
    }
};
user.greet();

Output: Hello Deepak

Another Example:

const calculator = {
    add(a, b) { return a + b; },
    multiply(a, b) { return a * b; }
};
console.log(calculator.add(10, 20));

39. What is method chaining?

Method chaining means calling multiple methods one after another on the same object or result.

Example:

const result = "javascript"
   .toUpperCase()
   .split("")
   .reverse()
   .join("");
console.log(result);

Output: TPIRCSAVAJ

Array Example:

const result = [1, 2, 3, 4, 5]
   .filter(num => num % 2 === 0)
   .map(num => num * 10);
console.log(result);

Output: [20,40]

Common Uses: Array processing, String manipulation, Promise chains, Libraries such as jQuery

40. What is object freezing and sealing?

JavaScript provides Object.freeze() and Object.seal() to restrict modifications to objects.

Object.freeze()

Prevents: Adding properties, Removing properties, Changing existing properties

const user = { name: "Deepak", age: 25 };
Object.freeze(user);
user.age = 30;
user.city = "Pune";
console.log(user); // unchanged

Object.seal()

Prevents: Adding properties, Removing properties

But existing properties can still be modified.

const user = { name: "Deepak", age: 25 };
Object.seal(user);
user.age = 30;
console.log(user.age); // 30

Key Difference:

Object.freeze(): Cannot add, delete, or modify properties

Object.seal(): Cannot add or delete properties, but can modify existing ones

🔥 Interview Tip: Both methods are shallow — nested objects can still be modified unless they are separately frozen/sealed.

❤️ Double Tap For Part 5