js完整节流函数

//节流函数
//每隔一段时间触发
//第一次触发立即执行
//如果在间隔时间内触发，会在间隔末尾再执行一次
function throttle(callback, timmer) {
  let isFirst = true;
  let execDate = +new Date();
  let throttleId;
  return function () {
    if (isFirst) {
      callback();
      execDate = +new Date();
      isFirst = false;
    } else {
      const currentDate = +new Date();
      if (currentDate - execDate >= timmer) {
        callback();
        execDate = + new Date();
      } else {
        if (throttleId) {
          clearTimeout(throttleId)
        };
        const timeWait = execDate + timmer - (+new Date());
        throttleId = setTimeout(() => {
          callback();
          execDate = + new Date();
        }, timeWait)
      }
    }
  }
}