JavaScript Program to Calculate Area of Circle

To calculate the area of a circle in JavaScript, use the formula area = Math.PI * radius * radius where radius is the circle's radius.

Examples

Inputradius = 0

OutputArea: 0

Inputradius = 5

OutputArea: 78.53981633974483

Inputradius = 10.5

OutputArea: 346.3605900582744

How to Think About It

To find the area of a circle, you need the radius. The area is found by multiplying pi (about 3.14) by the radius squared. So, you take the radius, multiply it by itself, then multiply by pi to get the area.

Algorithm

1

Get the radius value from the user or input.

2

Calculate the area by multiplying Math.PI with radius squared.

3

Return or print the calculated area.

Code

javascript

const radius = 5;
const area = Math.PI * radius * radius;
console.log('Area:', area);

Output

Area: 78.53981633974483

Dry Run

Let's trace radius = 5 through the code

1

Assign radius

radius = 5

2

Calculate area

area = Math.PI * 5 * 5 = 3.141592653589793 * 25 = 78.53981633974483

3

Print area

Output: 'Area: 78.53981633974483'

radius	area
5	78.53981633974483

Why This Works

Step 1: Use radius as input

The radius is the distance from the center to the edge of the circle, which is needed to find the area.

Step 2: Apply area formula

The formula area = Math.PI * radius * radius calculates the space inside the circle.

Step 3: Output the result

Printing the area shows the final calculated value to the user.

Alternative Approaches

Using a function to calculate area

javascript

function calculateArea(radius) {
  return Math.PI * radius ** 2;
}
console.log('Area:', calculateArea(5));

This approach is reusable and cleaner for multiple radius values.

Using arrow function

javascript

const area = radius => Math.PI * radius * radius;
console.log('Area:', area(5));

Shorter syntax, good for quick calculations.

Complexity: O(1) time, O(1) space

Time Complexity

The calculation uses a fixed number of operations regardless of input size, so it is constant time O(1).

Space Complexity

Only a few variables are used, so space is constant O(1).

Which Approach is Fastest?

All approaches use the same formula and have constant time and space, but using a function improves code reuse and clarity.

Approach	Time	Space	Best For
Direct calculation	O(1)	O(1)	Simple one-time calculation
Function	O(1)	O(1)	Reusability and clarity
Arrow function	O(1)	O(1)	Concise syntax for quick use