vant/packages/waterfall/src/utils.js

export default {
  debounce(func, wait, immediate) {
    var timeout, args, context, timestamp, result;
    return function() {
      context = this;
      args = arguments;
      timestamp = new Date();
      var later = function() {
        var last = (new Date()) - timestamp;
        if (last < wait) {
          timeout = setTimeout(later, wait - last);
        } else {
          timeout = null;
          result = func.apply(context, args);
        }
      };
      if (!timeout) {
        timeout = setTimeout(later, wait);
      }
      return result;
    };
  },

  // 找到最近的触发滚动事件的元素
  getScrollEventTarget(element) {
    var currentNode = element;
    // bugfix, see http://w3help.org/zh-cn/causes/SD9013 and http://stackoverflow.com/questions/17016740/onscroll-function-is-not-working-for-chrome
    while (currentNode && currentNode.tagName !== 'HTML' && currentNode.tagName !== 'BODY' && currentNode.nodeType === 1) {
      var overflowY = this.getComputedStyle(currentNode).overflowY;
      if (overflowY === 'scroll' || overflowY === 'auto') {
        return currentNode;
      }
      currentNode = currentNode.parentNode;
    }
    return window;
  },

  // 判断元素是否被加入到页面节点内
  isAttached(element) {
    var currentNode = element.parentNode;
    while (currentNode) {
      if (currentNode.tagName === 'HTML') {
        return true;
      }
      if (currentNode.nodeType === 11) {
        return false;
      }
      currentNode = currentNode.parentNode;
    }
    return false;
  },

  // 获取滚动高度
  getScrollTop(element) {
    return 'scrollTop' in element ? element.scrollTop : element.pageYOffset;
  },

  // 获取元素距离顶部高度
  getElementTop(element) {
    if (element === window) {
      return this.getScrollTop(window);
    }
    return element.getBoundingClientRect().top + this.getScrollTop(window);
  },

  getVisibleHeight(element) {
    if (element === window) {
      return element.innerHeight;
    }

    return element.getBoundingClientRect().height;
  },

  getComputedStyle: document.defaultView.getComputedStyle.bind(document.defaultView)
};