# JavaScript: Calculate the area and perimeter of a circle

## JavaScript Object: Exercise-9 with Solution

Write a JavaScript program to calculate the area and perimeter of a circle. Create two methods to calculate the area and perimeter. The radius of the circle will be supplied by the user.

JavaScript: Area and circumference of a circle

In geometry, the area enclosed by a circle of radius r is πr2. Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter.

The circumference of a circle is the linear distance around its edge.

Why is the area of a circle of a circle pi times the square of the radius?

Sample Solution: -

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>Area and Perimeter of a circle</title>
<body>
</body>
</html>
```
```

JavaScript Code:

``````function circle(radius)
{
// area method
this.area = function ()
{
};
// perimeter method
this.perimeter = function ()
{
};
}
var c = new circle(3);
console.log('Area =', c.area().toFixed(2));
console.log('perimeter =', c.perimeter().toFixed(2));
```
```

Sample Output:

```Area = 28.27
VM1407:17 perimeter = 18.85
```

Flowchart:

Live Demo:

See the Pen javascript-object-exercise-9 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.

﻿

## JavaScript: Tips of the Day

instance

```class Calc {
constructor() {
this.count = 0
}

increase() {
this.count ++
}
}

const calc = new Calc()
new Calc().increase()

console.log(calc.count)
```

We set the variable calc equal to a new instance of the Calc class. Then, we instantiate a new instance of Calc, and invoke the increase method on this instance. Since the count property is within the constructor of the Calc class, the count property is not shared on the prototype of Calc. This means that the value of count has not been updated for the instance calc points to, count is still 0.

Ref: https://bit.ly/2Hcpkm6