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

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