What is the `keyof` operator in TypeScript?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of TypeScript conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
The keyof operator in TypeScript is used to get a union type of all the keys (property names) of an object type. It allows you to access and use the keys of an object type as string literals in type operations and transformations.
interface Person {
name: string;
age: number;
}
type PersonKeys = keyof Person;
const key1: PersonKeys = 'name'; //Valid key
const key3: PersonKeys = 'address'; //Error
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.