JavaScript Program to Calculate Area of Triangle

You can calculate the area of a triangle in JavaScript using the formula area = 0.5 * base * height. For example, const area = 0.5 * base * height; calculates the area when you know the base and height.

Examples

Inputbase = 4, height = 3

OutputArea = 6

Inputbase = 10, height = 5

OutputArea = 25

Inputbase = 0, height = 5

OutputArea = 0

How to Think About It

To find the area of a triangle, you need to know its base length and height. The area is half the product of these two values. So, multiply the base by the height, then divide by 2 to get the area.

Algorithm

1

Get the base length of the triangle.

2

Get the height of the triangle.

3

Multiply the base by the height.

4

Divide the result by 2 to get the area.

5

Return or print the area.

Code

javascript

const base = 5;
const height = 8;
const area = 0.5 * base * height;
console.log('Area =', area);

Output

Area = 20

Dry Run

Let's trace the example where base = 5 and height = 8 through the code.

1

Assign base

base = 5

2

Assign height

height = 8

3

Calculate area

area = 0.5 * 5 * 8 = 20

4

Print area

Output: Area = 20

Step	Variable	Value
1	base	5
2	height	8
3	area	20
4	output	Area = 20

Why This Works

Step 1: Use base and height

The formula for the area of a triangle is 0.5 * base * height, so we need these two values.

Step 2: Multiply base and height

Multiplying base by height gives the area of a rectangle covering the triangle.

Step 3: Divide by 2

Since a triangle is half of that rectangle, we multiply by 0.5 to get the triangle's area.

Alternative Approaches

Using a function

javascript

function triangleArea(base, height) {
  return 0.5 * base * height;
}
console.log('Area =', triangleArea(5, 8));

This makes the code reusable for different base and height values.

Using Heron's formula

javascript

function heronArea(a, b, c) {
  const s = (a + b + c) / 2;
  return Math.sqrt(s * (s - a) * (s - b) * (s - c));
}
console.log('Area =', heronArea(3, 4, 5));

This calculates area when you know all three sides, but is more complex.

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

Time Complexity

The calculation uses a fixed number of arithmetic operations, so it runs in constant time.

Space Complexity

Only a few variables are used, so the space needed is constant.

Which Approach is Fastest?

The direct formula is fastest and simplest; Heron's formula is slower due to square root and more inputs.

Approach	Time	Space	Best For
Direct formula (0.5 * base * height)	O(1)	O(1)	Known base and height
Function wrapper	O(1)	O(1)	Reusable calculations
Heron's formula	O(1)	O(1)	Known all three sides