JavaScript Object Methods and Programs

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In JavaScript, an Object is a non-primitive data type used to store data in key-value pairs.

Objects are one of the most important concepts in JavaScript because almost everything in JavaScript is based on objects.

1. Creating Objects

Using Object Literal (Most Common)

const person = {
    name: "John",
    age: 25,
    city: "New York"
};

console.log(person);

Using new Object()

const person = new Object();

person.name = "John";
person.age = 25;

console.log(person);

2. Accessing Object Properties

Dot Notation

console.log(person.name);
console.log(person.age);

Bracket Notation

console.log(person["name"]);
console.log(person["age"]);

Useful when property names are dynamic.

let key = "name";

console.log(person[key]);

3. Adding Properties

person.country = "USA";

console.log(person);

4. Updating Properties

person.age = 30;

console.log(person.age);

5. Deleting Properties

delete person.city;

console.log(person);

6. Nested Objects

const student = {
    name: "Sam",
    marks: {
        math: 90,
        science: 85
    }
};

console.log(student.marks.math);

7. Object Methods

Methods are functions inside objects.

const user = {
    name: "Alex",

    greet: function () {
        console.log("Hello");
    }
};

user.greet();

Important Object Methods

1. Object.keys()

Returns all object keys.

const person = {
    name: "John",
    age: 25
};

console.log(Object.keys(person));

Output:

["name", "age"]

2. Object.values()

Returns all values.

console.log(Object.values(person));

Output:

["John", 25]

3. Object.entries()

Returns key-value pairs as arrays.

console.log(Object.entries(person));

Output:

[
  ["name", "John"],
  ["age", 25]
]

4. Object.assign()

Copies properties from one object to another.

const obj1 = { a: 1 };
const obj2 = { b: 2 };

const result = Object.assign({}, obj1, obj2);

console.log(result);

Output:

{ a: 1, b: 2 }

5. Object.freeze()

Prevents modification.

const car = {
    brand: "BMW"
};

Object.freeze(car);

car.brand = "Audi";

console.log(car.brand);

Output:

BMW

6. Object.seal()

Allows updating existing properties but prevents adding/removing.

const user = {
    name: "John"
};

Object.seal(user);

user.name = "Sam"; // allowed
user.age = 30;     // not allowed

console.log(user);

7. Object.hasOwn()

Checks if property exists.

const person = {
    name: "John"
};

console.log(Object.hasOwn(person, "name"));

Output:

true

8. Object.create()

Creates a new object using another object as prototype.

const animal = {
    sound: "Bark"
};

const dog = Object.create(animal);

console.log(dog.sound);

9. Object.fromEntries()

Converts array to object.

const arr = [
    ["name", "John"],
    ["age", 25]
];

console.log(Object.fromEntries(arr));

Output:

{
  name: "John",
  age: 25
}

10. Object.is()

Compares two values.

console.log(Object.is(10, 10));

Output:

true

Looping Through Objects

Using for...in

const person = {
    name: "John",
    age: 25
};

for (let key in person) {
    console.log(key, person[key]);
}

Object Destructuring

const person = {
    name: "John",
    age: 25
};

const { name, age } = person;

console.log(name);
console.log(age);

Spread Operator with Objects

const obj1 = {
    a: 1
};

const obj2 = {
    ...obj1,
    b: 2
};

console.log(obj2);

Shallow Copy vs Reference

Reference Copy

const obj1 = {
    name: "John"
};

const obj2 = obj1;

obj2.name = "Sam";

console.log(obj1.name);

Output:

Sam

Shallow Copy

const obj1 = {
    name: "John"
};

const obj2 = { ...obj1 };

obj2.name = "Sam";

console.log(obj1.name);

Output:

John

Real-World Example

const employee = {
    id: 101,
    name: "David",
    department: "QA",
    skills: ["JavaScript", "Playwright"],

    displayInfo() {
        console.log(`${this.name} works in ${this.department}`);
    }
};

employee.displayInfo();

Common Interview Questions

Difference Between Object and Array

ObjectArray
Stores key-value pairsStores ordered values
Uses keysUses indexes
{}[]

Difference Between == and Object.is()

console.log(NaN == NaN); // false
console.log(Object.is(NaN, NaN)); // true

Practice Programs

1. Count Object Properties

const user = {
    name: "John",
    age: 25,
    city: "NY"
};

console.log(Object.keys(user).length);

2. Merge Two Objects

const a = { x: 1 };
const b = { y: 2 };

const c = { ...a, ...b };

console.log(c);

3. Convert Object to Array

const person = {
    name: "John",
    age: 25
};

console.log(Object.entries(person));

Summary

JavaScript objects are used to:

  • Store structured data
  • Create reusable methods
  • Represent real-world entities
  • Manage application state

Most commonly used object methods:

  • Object.keys()
  • Object.values()
  • Object.entries()
  • Object.assign()
  • Object.freeze()
  • Object.seal()
  • Object.hasOwn()

10 JavaScript Object Programs with Solutions

1. Count Number of Properties in an Object

Problem

Find total number of keys in an object.

Solution

const user = {
    name: "John",
    age: 25,
    city: "New York"
};

const count = Object.keys(user).length;

console.log(count);

Output

3

2. Iterate Through Object Properties

Problem

Print all keys and values from an object.

Solution

const student = {
    name: "Sam",
    marks: 90,
    grade: "A"
};

for (let key in student) {
    console.log(key + " : " + student[key]);
}

Output

name : Sam
marks : 90
grade : A

3. Merge Two Objects

Problem

Combine two objects into one.

Solution

const obj1 = {
    a: 1,
    b: 2
};

const obj2 = {
    c: 3,
    d: 4
};

const merged = { ...obj1, ...obj2 };

console.log(merged);

Output

{
  a: 1,
  b: 2,
  c: 3,
  d: 4
}

4. Check if Property Exists

Problem

Check whether a key exists in object.

Solution

const employee = {
    id: 101,
    name: "David"
};

console.log("name" in employee);
console.log("salary" in employee);

Output

true
false

5. Remove Property from Object

Problem

Delete a property from object.

Solution

const car = {
    brand: "BMW",
    color: "Black"
};

delete car.color;

console.log(car);

Output

{
  brand: "BMW"
}

6. Convert Object to Array

Problem

Convert object into array of key-value pairs.

Solution

const person = {
    name: "John",
    age: 30
};

const result = Object.entries(person);

console.log(result);

Output

[
  ["name", "John"],
  ["age", 30]
]

7. Find Sum of Object Values

Problem

Calculate sum of numeric values in object.

Solution

const marks = {
    math: 90,
    science: 80,
    english: 85
};

let sum = 0;

for (let key in marks) {
    sum += marks[key];
}

console.log(sum);

Output

255

8. Clone an Object

Problem

Create copy of object without affecting original.

Solution

const original = {
    name: "Alex",
    age: 28
};

const copy = { ...original };

copy.name = "Sam";

console.log(original);
console.log(copy);

Output

{ name: "Alex", age: 28 }

{ name: "Sam", age: 28 }

9. Freeze an Object

Problem

Prevent object modification.

Solution

const user = {
    name: "John"
};

Object.freeze(user);

user.name = "Sam";

console.log(user.name);

Output

John

10. Nested Object Access

Problem

Access values inside nested objects.

Solution

const company = {
    name: "TechSoft",
    employee: {
        id: 101,
        details: {
            name: "David",
            role: "QA Engineer"
        }
    }
};

console.log(company.employee.details.name);
console.log(company.employee.details.role);

Output

David
QA Engineer

Bonus Program — Object Destructuring

Problem

Extract object properties into variables.

Solution

const user = {
    name: "John",
    age: 25
};

const { name, age } = user;

console.log(name);
console.log(age);

Output

John
25

Concepts Covered

These programs cover:

  • Object creation
  • Object iteration
  • Object methods
  • Nested objects
  • Destructuring
  • Spread operator
  • Property checking
  • Cloning
  • Freezing objects
  • Data transformation

Beginner Interview Programs

1. Find the Employee with the Highest Salary

Scenario

A company stores employee details in an object. Find the employee who has the highest salary.

Input

const employees = {
    emp1: { name: "John", salary: 55000 },
    emp2: { name: "Alice", salary: 72000 },
    emp3: { name: "David", salary: 68000 }
};

Expected Output

Highest Salary Employee:
Alice
Salary: 72000

2. Count Product Categories

Scenario

An online shopping website stores products with categories. Count how many products belong to each category.

Input

const products = {
    p1: { category: "Electronics" },
    p2: { category: "Furniture" },
    p3: { category: "Electronics" },
    p4: { category: "Books" },
    p5: { category: "Books" }
};

Expected Output

Electronics : 2
Furniture : 1
Books : 2

3. Merge Student Information

Scenario

Merge two student objects into one object.

Input

const personal = {
    name: "Rahul",
    age: 21
};

const academic = {
    course: "B.Tech",
    marks: 88
};

Expected Output

{
    name: "Rahul",
    age: 21,
    course: "B.Tech",
    marks: 88
}

4. Find Missing Properties

Scenario

Check whether every employee object contains an email property.

Input

const employees = {
    emp1: {
        name: "John",
        email: "john@test.com"
    },
    emp2: {
        name: "Alice"
    },
    emp3: {
        name: "David",
        email: "david@test.com"
    }
};

Expected Output

Employee Missing Email:
Alice

5. Calculate Total Shopping Cart Value

Scenario

Calculate the total bill of all products in the shopping cart.

Input

const cart = {
    item1: {
        name: "Mouse",
        price: 700,
        quantity: 2
    },
    item2: {
        name: "Keyboard",
        price: 1200,
        quantity: 1
    },
    item3: {
        name: "Monitor",
        price: 9500,
        quantity: 1
    }
};

Expected Output

Total Cart Value:
12100

6. Remove Null Values from Object

Scenario

Remove all properties whose value is null.

Input

const user = {
    name: "Deepesh",
    phone: null,
    city: "Bhopal",
    email: null,
    age: 30
};

Expected Output

{
    name: "Deepesh",
    city: "Bhopal",
    age: 30
}

7. Find Duplicate Values

Scenario

Identify duplicate values present in an object.

Input

const students = {
    s1: "A",
    s2: "B",
    s3: "A",
    s4: "C",
    s5: "B"
};

Expected Output

Duplicate Values:
A
B

8. Convert Object into Sorted Array

Scenario

Convert the object values into an array and sort them in ascending order.

Input

const marks = {
    maths: 78,
    science: 91,
    english: 65,
    computer: 99
};

Expected Output

[65, 78, 91, 99]

9. Update Nested Object

Scenario

Update the city of the employee.

Input

const employee = {
    id: 101,
    name: "John",
    address: {
        city: "Delhi",
        state: "Delhi"
    }
};

Task

Update city to Mumbai.

Expected Output

{
    id:101,
    name:"John",
    address:{
        city:"Mumbai",
        state:"Delhi"
    }
}

10. Find Average Salary

Scenario

Calculate the average salary of all employees.

Input

const employees = {
    emp1: { salary: 45000 },
    emp2: { salary: 60000 },
    emp3: { salary: 75000 },
    emp4: { salary: 50000 }
};

Expected Output

Average Salary:
57500

11. Inventory Stock Checker

Scenario

Display all products whose quantity is less than 5.

Input

const inventory = {
    p1: { name: "Laptop", quantity: 3 },
    p2: { name: "Keyboard", quantity: 8 },
    p3: { name: "Mouse", quantity: 2 },
    p4: { name: "Monitor", quantity: 10 }
};

Expected Output

Low Stock Products:
Laptop
Mouse

12. Group Employees by Department

Scenario

Group employees based on department.

Input

const employees = {
    emp1: { name: "John", department: "IT" },
    emp2: { name: "Alice", department: "HR" },
    emp3: { name: "David", department: "IT" },
    emp4: { name: "Emma", department: "Finance" }
};

Expected Output

{
    IT: ["John", "David"],
    HR: ["Alice"],
    Finance: ["Emma"]
}

13. Find the Most Expensive Product

Scenario

Find the product with the highest price.

Input

const products = {
    p1: { name: "Phone", price: 25000 },
    p2: { name: "Laptop", price: 65000 },
    p3: { name: "Watch", price: 12000 }
};

Expected Output

Laptop
65000

14. Count Boolean Values

Scenario

Count how many properties have true and false values.

Input

const permissions = {
    read: true,
    write: false,
    delete: true,
    update: false,
    share: true
};

Expected Output

True : 3
False : 2

15. Reverse Key-Value Pairs

Scenario

Swap the keys and values of an object.

Input

const countryCodes = {
    India: "IN",
    America: "US",
    Japan: "JP"
};

Expected Output

{
    IN: "India",
    US: "America",
    JP: "Japan"
}

16. Find Employees Joined After 2022

Scenario

A company stores employee joining years. Display the employees who joined after 2022.

Input

const employees = {
    emp1: { name: "John", joiningYear: 2021 },
    emp2: { name: "Alice", joiningYear: 2023 },
    emp3: { name: "David", joiningYear: 2024 },
    emp4: { name: "Emma", joiningYear: 2022 }
};

Expected Output

Employees Joined After 2022
---------------------------
Alice
David

17. Update Product Prices by Percentage

Scenario

An e-commerce application increases all product prices by 10%.

Input

const products = {
    p1: { name: "Laptop", price: 50000 },
    p2: { name: "Mouse", price: 800 },
    p3: { name: "Keyboard", price: 1500 }
};

Expected Output

Updated Prices

Laptop : 55000
Mouse : 880
Keyboard : 1650

18. Find Customers with Premium Membership

Scenario

Display only customers whose membership type is Premium.

Input

const customers = {
    c1: { name: "Rahul", membership: "Premium" },
    c2: { name: "Amit", membership: "Regular" },
    c3: { name: "Neha", membership: "Premium" },
    c4: { name: "Priya", membership: "Regular" }
};

Expected Output

Premium Customers

Rahul
Neha

19. Count Active Users

Scenario

Count how many users are active and inactive.

Input

const users = {
    u1: { name: "John", active: true },
    u2: { name: "Alice", active: false },
    u3: { name: "David", active: true },
    u4: { name: "Emma", active: true }
};

Expected Output

Active Users : 3

Inactive Users : 1

20. Find the Oldest Employee

Scenario

Find the employee with the maximum age.

Input

const employees = {
    emp1: { name: "John", age: 30 },
    emp2: { name: "Alice", age: 42 },
    emp3: { name: "David", age: 38 },
    emp4: { name: "Emma", age: 27 }
};

Expected Output

Oldest Employee

Alice

Age : 42

21. Generate Student Report Card

Scenario

Calculate total, average, percentage, and grade for each student.

Input

const students = {
    s1: {
        name: "Rahul",
        maths: 90,
        science: 85,
        english: 88
    },
    s2: {
        name: "Priya",
        maths: 75,
        science: 80,
        english: 70
    }
};

Expected Output

Student : Rahul

Total : 263

Average : 87.67

Grade : A

---------------------

Student : Priya

Total : 225

Average : 75

Grade : B

22. Find Duplicate Email Addresses

Scenario

Identify duplicate email addresses stored in employee records.

Input

const employees = {
    emp1: { email: "john@test.com" },
    emp2: { email: "alice@test.com" },
    emp3: { email: "john@test.com" },
    emp4: { email: "emma@test.com" }
};

Expected Output

Duplicate Emails

john@test.com

23. Sort Employees by Salary

Scenario

Display employees in ascending order of salary.

Input

const employees = {
    emp1: { name: "John", salary: 65000 },
    emp2: { name: "Alice", salary: 48000 },
    emp3: { name: "David", salary: 72000 },
    emp4: { name: "Emma", salary: 55000 }
};

Expected Output

Alice : 48000

Emma : 55000

John : 65000

David : 72000

24. Calculate Total Inventory Value

Scenario

Calculate inventory value using price × quantity.

Input

const inventory = {
    p1: { name: "Laptop", price: 50000, quantity: 4 },
    p2: { name: "Mouse", price: 800, quantity: 15 },
    p3: { name: "Keyboard", price: 1500, quantity: 10 }
};

Expected Output

Total Inventory Value

227000

25. Find Employees Working in Multiple Skills

Scenario

Display employees having more than two skills.

Input

const employees = {
    emp1: {
        name: "John",
        skills: ["JavaScript", "React"]
    },
    emp2: {
        name: "Alice",
        skills: ["Java", "Spring", "Docker"]
    },
    emp3: {
        name: "David",
        skills: ["Python", "Django", "AWS", "Docker"]
    }
};

Expected Output

Employees with More Than 2 Skills

Alice

David

26. Create an Employee Directory

Scenario

Convert employee objects into a formatted directory.

Input

const employees = {
    emp1: {
        name: "John",
        phone: "9876543210"
    },
    emp2: {
        name: "Alice",
        phone: "9876500000"
    }
};

Expected Output

Employee Directory

John - 9876543210

Alice - 9876500000

27. Find Products Above Average Price

Scenario

Display products priced above the average price.

Input

const products = {
    p1: { name: "Laptop", price: 60000 },
    p2: { name: "Mouse", price: 900 },
    p3: { name: "Keyboard", price: 2000 },
    p4: { name: "Monitor", price: 18000 }
};

Expected Output

Average Price

20225

Products Above Average

Laptop

Monitor

28. Validate Employee Records

Scenario

Find employees whose records are missing mandatory fields such as name, email, or department.

Input

const employees = {
    emp1: {
        name: "John",
        email: "john@test.com",
        department: "IT"
    },
    emp2: {
        name: "Alice",
        department: "HR"
    },
    emp3: {
        email: "david@test.com",
        department: "Finance"
    }
};

Expected Output

Invalid Records

Alice : Missing Email

Employee 3 : Missing Name

29. Compare Two Objects

Scenario

Compare two employee objects and identify differing properties.

Input

const employee1 = {
    id: 101,
    name: "John",
    salary: 50000
};

const employee2 = {
    id: 101,
    name: "John",
    salary: 60000
};

Expected Output

Different Property

salary

Employee1 : 50000

Employee2 : 60000

30. Build a Sales Dashboard

Scenario

Calculate sales statistics for different regions.

Input

const sales = {
    north: 250000,
    south: 180000,
    east: 320000,
    west: 210000
};

Expected Output

Total Sales : 960000

Average Sales : 240000

Highest Sales : East (320000)

Lowest Sales : South (180000)

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