Debounce Interview Questions (Flipkart)

Debounce Interview Questions (Flipkart)

Q1: Implement debounce from scratch.

function debounce(fn, delay) {
  let timer;
  return function (...args) {
    clearTimeout(timer);
    timer = setTimeout(() => fn.apply(this, args), delay);
  };
}

Q2: How does debounce work internally?

Each call clears the previous timer and sets a new one. Only the last call within the delay period executes. The timer variable is kept alive by a closure.

Q3: What is the difference between debounce and throttle?

Debounce: delays until activity stops (search input). Throttle: limits to once per interval (scroll handler).

Q4: How do you test debounce?

Call the debounced function rapidly. Verify that only the last call executes after the delay. Use jest.useFakeTimers() in unit tests.

Q5: How do you add a cancel method?

debounced.cancel = () => clearTimeout(timer);

The Takeaway

Flipkart debounce questions: implement from scratch (closure + clearTimeout + setTimeout), explain how it works (last call wins), difference from throttle, how to test (fake timers), and cancel method.