Overview

Implement throttle(fn, delay) — returns a throttled function that invokes fn at most once per delay ms. The first call fires immediately.

Constraints

• First invocation fires immediately
• Subsequent calls during cooldown are ignored
• Uses leading-edge throttling

Solution

function throttle(fn, delay) {
  let lastTime = 0;
  return function(...args) {
    const now = Date.now();
    if (now - lastTime >= delay) {
      lastTime = now;
      return fn.apply(this, args);
    }
  };
}