What is the output of below function calls?
Assesses fundamental understanding of JavaScript conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Code snippet:
const circle = {
radius: 20,
diameter() {
return this.radius * 2;
},
perimeter: () => 2 * Math.PI * this?.radius,
};
console.log(circle.diameter());
console.log(circle.perimeter());
Output:
The output is 40 and NaN. Remember that diameter is a regular function, whereas the value of perimeter is an arrow function. The this keyword of a regular function(i.e, diameter) refers to the surrounding scope which is a class(i.e, Shape object). Whereas this keyword of perimeter function refers to the surrounding scope which is a window object. Since there is no radius property on window objects it returns an undefined value and the multiple of number value returns NaN value.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.