4 questions developers actually get asked about debouncing & throttling — with clear, practical answers you can use to prepare.
Debouncing is a technique that delays running a function until a burst of repeated events has stopped for a set amount of time. For example, a search box that fires an API call 300ms after the user stops typing, not on every keystroke. It is used when you only care about the final state after activity settles, so you avoid redundant work while the user is still going.
Throttling is a technique that limits how often a function can run, no matter how many times it is triggered. A throttled scroll handler set to 200ms will run at most five times per second even if the browser fires hundreds of scroll events. It is used when you need steady updates during continuous activity, like scroll-driven animations or live drag handlers.
Debouncing waits for a pause and then fires once: good when only the final action matters (search input, auto-save, form validation). Throttling fires on a fixed cadence regardless of event volume: good when you need regular updates during continuous activity (scroll, resize, mouse drag). A simple rule of thumb: if the event comes in bursts that should collapse to one call, debounce; if the event is continuous and you want a steady sampling rate, throttle.
Avoid them on actions the user expects to happen instantly, like Submit, Buy, or Delete buttons. Debouncing a checkout button would feel broken, and if double-clicks are the worry, disabling the button after the first click is a cleaner fix. Also skip them when events are already infrequent, since adding a timer just introduces lag without reducing load.
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