手写防抖(debounce)和节流(throttle)带配置

function debounce(fn, delay = 300, immediate = false) {
  let timer = null;
  return function(...args) {
    const callNow = immediate && !timer;
    clearTimeout(timer);
    timer = setTimeout(() => {
      timer = null;
      if (!immediate) fn.apply(this, args);
    }, delay);
    if (callNow) fn.apply(this, args);
  };
}

function throttle(fn, delay = 300, options = { leading: true, trailing: true }) {
  let timer = null, lastArgs = null;
  return function(...args) {
    const context = this;
    if (!timer) {
      if (options.leading) fn.apply(context, args);
      timer = setTimeout(() => {
        timer = null;
        if (options.trailing && lastArgs) {
          fn.apply(context, lastArgs);
          lastArgs = null;
        }
      }, delay);
    } else {
      lastArgs = args;
    }
  };
}

区别：防抖等待静止后才执行；节流保证固定时间间隔执行。