What is iterator in JavaScript?
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.
In JavaScript, an iterator is an object that provides a way to access elements of a collection or a custom data structure in a sequential manner. It allows you to loop over the elements one at a time, retrieving them on demand.
The most important method is next(), which is responsible for returning the next element in the sequence. When you call next() on an iterator, it returns an object with two properties: value, representing the current element, and done, indicating whether there are more elements or if the iteration is complete.
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.