手写throttle

1.普通版（立即执行）

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

2.延迟执行

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

3.支持立即执行和尾调用

function throttle(fn, delay, options = {}) {
  let timerId = null;
  let lastRunTime = 0;
  const { leading = true, trailing = false } = options; // 默认立即执行，不尾调用

  return function (...args) {
    const now = Date.now();
    const remaining = delay - (now - lastRunTime);

    if (remaining <= 0) {
      // 冷却期已过，可以执行
      if (timerId) {
        clearTimeout(timerId);
        timerId = null;
      }
      if (leading) {
        fn.apply(this, args);
      }
      lastRunTime = now;
    } else if (!timerId && trailing) {
      // 处于冷却期内，且允许尾调用，设置定时器用于尾执行
      timerId = setTimeout(() => {
        fn.apply(this, args);
        lastRunTime = Date.now();
        timerId = null;
      }, remaining);
    }
  };
}