What is the Output of this Code?

Given the following method calls in JavaScript, what is the output?

const circle = {
    radius: 10,
    diameter() {
        return this.radius * 2;
    },

    perimeter: () => 2 * Math.PI * this.radius
};

circle.diameter();
circle.perimeter();

The correct answer is NaN. circle.diameter executes without the problem but perimeter is defined as an arrow function. Arrow functions don’t bind their own context which means this.radius will be undefined. And 2 * Math.PI * undefined will be equal to NaN.

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Resources:

• Arrow function expression in JavaScript
• The this keyword