Object

Question 1

What is an object in JavaScript?

Answer 1

A collection of key-value pairs used to store related data and functions.

Question 2

How do you create an object literal?

Answer 2

Use curly braces {}. Example: const person = { name: 'John', age: 30 };

Question 3

How do you access an object property?

Answer 3

Use dot or bracket notation. Example: person.name or person['name'];

Question 4

How do you add a new property to an object?

Answer 4

Assign a value to a new key. Example: person.job = 'Designer';

Question 5

How do you remove a property from an object?

Answer 5

Use the delete keyword. Example: delete person.age;

Question 6

How do you check if an object has a property?

Answer 6

Use the in operator or .hasOwnProperty(). Example: 'name' in person or person.hasOwnProperty('name');

Question 7

How do you loop through object properties?

Answer 7

Use a for...in loop. Example: for (let key in person) { console.log(key, person[key]); }

Question 8

How do you get all property names from an object?

Answer 8

Use Object.keys(obj). Example: Object.keys(person);

Question 9

How do you get all property values from an object?

Answer 9

Use Object.values(obj). Example: Object.values(person);

Question 10

How do you get both keys and values from an object?

Answer 10

Use Object.entries(obj). Example: Object.entries(person);

Question 11

How do you merge multiple objects?

Answer 11

Use Object.assign(target, ...sources) or the spread operator {...obj1, ...obj2}.

Question 12

How do you create a shallow copy of an object?

Answer 12

Use {...obj} or Object.assign({}, obj);

Question 13

How do you freeze an object to make it immutable?

Answer 13

Use Object.freeze(obj);

Question 14

How do you prevent adding or removing properties to an object?

Answer 14

Use Object.seal(obj);

Question 15

How do you create a new object with a specific prototype?

Answer 15

Use Object.create(proto);

Question 16

How do you get the prototype of an object?

Answer 16

Use Object.getPrototypeOf(obj);

Question 17

How do you define methods inside an object?

Answer 17

Use function expressions or shorthand syntax. Example: const person = { greet() { console.log('Hi'); } };

Question 18

What does this refer to inside an object method?

Answer 18

It refers to the object that the method belongs to.

Question 19

How do you convert an object to a JSON string?

Answer 19

Use JSON.stringify(obj);

Question 20

How do you parse a JSON string back to an object?

Answer 20

Use JSON.parse(jsonString);

Question 21

What is destructuring in objects?

Answer 21

Extracting values from objects into variables. Example: const { name, age } = person;

Question 22

How do you rename a property while destructuring?

Answer 22

Use a colon. Example: const { name: fullName } = person;

Question 23

How do you provide a default value during destructuring?

Answer 23

Use =. Example: const { age = 25 } = person;

Question 24

How do you check if two objects are equal?

Answer 24

Compare their keys and values manually or use JSON.stringify(obj1) === JSON.stringify(obj2);

Question 25

What is the difference between a shallow and deep copy?

Answer 25

A shallow copy only copies the first level; a deep copy recursively copies nested objects.

Question 26

How do you deep copy an object?

Answer 26

Use `structuredClone(obj)` or `JSON.parse(JSON.stringify(obj));`

Question 27

How do you get the number of properties in an object?

Answer 27

Use `Object.keys(obj).length;`

Question 28

How do you define getters and setters in an object?

Answer 28

Use `get` and `set` keywords. Example: `get name() { return this._name; } set name(n) { this._name = n; }`

Question 29

How do you convert an array of key-value pairs into an object?

Answer 29

Use `Object.fromEntries(array);`

Question 30

What is optional chaining?

Answer 30

It allows safe property access using `?.`. Example: `person.address?.city;` returns undefined if address doesn’t exist.