#432 Throttle with Leading and Trailing

Implement a utility function throttle that limits how often a target function can be invoked, supporting both leading and trailing execution.

Requirements

• Signature:

  function throttle<T extends (...args: any[]) => any>(
    fn: T,
    delay: number,
    options?: {
      leading?: boolean;  // default = true
      trailing?: boolean; // default = true
    },
  ): (...args: Parameters<T>) => ReturnType<T>
  
  

• Leading call — if leading is true, the target function is invoked immediately on the first call.

• Trailing call — if trailing is true, the target function is invoked once more with the last arguments after the delay elapses.

• Subsequent calls within the delay window are ignored except for updating the arguments for the trailing call.

• If both leading and trailing are false, the wrapper should behave as a no-op throttle (simply returning fn).

• Return value for throttled calls should match the return type of fn when a call is actually executed; otherwise undefined.

Example

const fn = jest.fn();
const throttled = throttle(fn, 100, { leading: true, trailing: true });

throttled('A'); // executes immediately → fn('A')
throttled('B'); // ignored, but stores args for trailing

// after ~100 ms → fn('B') executes once