列表自动滚动效果，若手动滚轮，则是手动滚动效果

默认自动上滚，当鼠标移入后，停止滚动；鼠标移除，又恢复自动滚动；鼠标移入后，绑定mousewheel，可以滚轮手动上下滚动。

//lh---每行列表的高度，speed---滚动的速度，delay---间隔多久滚动一次,marqueeDOM---需要实现这个效果的dom, overflowY--超出部分的高度
export const listAutoScroll = (lh, speed, delay, marqueeObj, overflow_Y) => { 
  let p = false;
  let t;
  let o = marqueeObj;
  let overflowY = overflow_Y;
  // o.innerHTML += o.innerHTML; // 首尾相接的自动滚动
  o.style.marginTop = 0;
  
  //鼠标移入，停止滚动
  o.onmouseover = function () {
    p = true;
    on(o, 'mousewheel', handleMousewheel);
  }; 

  //鼠标移出，继续滚动
  o.onmouseout = function (e) {
    p = false;
    off(o, 'mousewheel', handleMousewheel);
  }; 



  function start() {
    t = setInterval(scrolling, speed); //定时器，自动滚动
    if (!p) o.style.marginTop = parseInt(o.style.marginTop) - 1 + "px";
  }

  function scrolling() {
    if (parseInt(o.style.marginTop) % lh != 0) {
      o.style.marginTop = parseInt(o.style.marginTop) - 1 + "px";
      if (Math.abs(parseInt(o.style.marginTop)) >= o.scrollHeight) {
        o.style.marginTop = 0;
      }
    } else {
      clearInterval(t);
      setTimeout(start, delay);
    }
  }

  function handleMousewheel(event) {
    const e = event || window.event;
    e.preventDefault();
    // p = true;
    let wheelDeltaY = e.wheelDeltaY || e.detail;
    let dis = wheelDeltaY / 120; 

    o.style.marginTop = parseInt(o.style.marginTop) + dis * lh + 'px';

    if(dis > 0 && parseInt(o.style.marginTop) >= 0) {
      o.style.marginTop = '0px';
    }
    if(dis < 0 && parseInt(o.style.marginTop) <= (-1) * (overflowY)) {
      o.style.marginTop = `${-1 * overflowY}px`;
    }
  }

  setTimeout(start, delay);
};
// listAutoScroll(40, 20, 1000, "marqueebox"); // 方法调用

/**
 * @description 绑定事件 on(element, event, handler)
 */
export const on = (function () {
  if (document.addEventListener) {
    return function (element, event, handler) {
      if (element && event && handler) {
        element.addEventListener(event, handler, false);
      }
    };
  } else {
    return function (element, event, handler) {
      if (element && event && handler) {
        element.attachEvent('on' + event, handler);
      }
    };
  }
})();

/**
 * @description 解绑事件 off(element, event, handler)
 */
export const off = (function () {
  if (document.removeEventListener) {
    return function (element, event, handler) {
      if (element && event) {
        element.removeEventListener(event, handler, false);
      }
    };
  } else {
    return function (element, event, handler) {
      if (element && event) {
        element.detachEvent('on' + event, handler);
      }
    };
  }
})();