[Improvement] reduce scroll utils (#1112)

packages/utils/scroll.js

@@ -1,33 +1,7 @@
-import { isServer } from './index';
+import { isServer } from './';
 
 export default {
-  debounce(func, wait, immediate) {
+  // get nearest scroll element
-    let timeout, args, context, timestamp, result;
-    return function() {
-      context = this;
-      args = arguments;
-      timestamp = new Date();
-      const later = () => {
-        const 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
-   * @param {Element} element
-	 * @param {Element} rootElement
-	 * @return {Element | window}
-   */
   getScrollEventTarget(element, rootParent = window) {
     let currentNode = element;
     // bugfix, see http://w3help.org/zh-cn/causes/SD9013 and http://stackoverflow.com/questions/17016740/onscroll-function-is-not-working-for-chrome
@@ -41,32 +15,15 @@ export default {
     return rootParent;
   },
 
-  // 判断元素是否被加入到页面节点内
-  isAttached(element) {
-    let 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;
   },
 
-  // 设置滚动高度
   setScrollTop(element, value) {
     'scrollTop' in element ? element.scrollTop = value : element.scrollTo(element.scrollX, value);
   },
 
-  // 获取元素距离顶部高度
+  // get distance from element top to page top
   getElementTop(element) {
     return (element === window ? 0 : element.getBoundingClientRect().top) + this.getScrollTop(window);
   },

packages/waterfall/directive.js

@@ -12,7 +12,7 @@ function doBindEvent() {
   }
   this.el[CONTEXT].binded = true;
 
-  this.scrollEventListener = Utils.debounce(handleScrollEvent.bind(this), 200);
+  this.scrollEventListener = handleScrollEvent.bind(this);
   this.scrollEventTarget = Utils.getScrollEventTarget(this.el);
 
   const disabledExpr = this.el.getAttribute('waterfall-disabled');
@@ -78,10 +78,8 @@ function handleScrollEvent() {
 function startBind(el) {
   const context = el[CONTEXT];
 
-  context.vm.$nextTick(function() {
+  context.vm.$nextTick(() => {
-    if (Utils.isAttached(el)) {
     doBindEvent.call(el[CONTEXT]);
-    }
   });
 }