Throttle II

Throttling caps how often a function runs — at most once per interval — no matter how fast it's called. This version adds the controls real code needs: leading/trailing edge options that decide when within each window the call fires, and cancel/flush methods to drop or force a pending call.

Implement throttle(fn, wait, options). By default it fires on both the leading edge (immediately) and the trailing edge (once more after wait, if there were calls during the window). leading: false skips the immediate call; trailing: false skips the final one. Expose .cancel() and .flush().

Signature

function throttle(fn, wait, options) {
  // options: { leading = true, trailing = true }
  // returns a throttled fn with .cancel() and .flush()
}

Examples

// Fires at most once per 100ms while scrolling — immediately, then trailing:
const onScroll = throttle(update, 100);

throttle(save, 1000, { leading: false }); // wait 1s, then fire (no immediate)
throttle(log, 1000, { trailing: false });  // fire immediately, ignore the rest
onScroll.cancel(); // drop a pending trailing call (e.g. on unmount)

Notes

• Leading edge — with leading: true (default), the first call in a window fires fn immediately.
• Trailing edge — with trailing: true (default), a final call fires after wait, using the latest arguments, if any calls arrived during the window.
• At most once per wait — between the edges, extra calls are collapsed.
• cancel() — clears any pending trailing call so it never fires.
• flush() — invokes a pending trailing call right now instead of waiting.