优化滚动组件;下拉组件

src/form/dropdown.wc

@@ -241,6 +241,8 @@ export default class Dropdown {
       this.state.optionShow = false
       this.__OPTIONS__.classList.toggle('active', false)
     })
+
+    $.nextTick(_ => this._updateChildrenStat())
   }
 
   unmounted() {

src/form/option.wc

@@ -119,7 +119,11 @@ export default class Option {
     switch (name) {
       case 'value':
       case 'label':
+        if (val === null) {
+          this[name] = ''
+        } else {
           this[name] = val
+        }
         break
 
       case 'disabled':

src/markd/index.wc

@@ -209,7 +209,9 @@ export default class Markd {
     } else {
       this.__BOX__.innerHTML = ''
     }
-    this.dispatchEvent(new CustomEvent('ready', { bubbles: true }))
+    this.dispatchEvent(
+      new CustomEvent('ready', { bubbles: true, cancelable: true })
+    )
   }
 
   clear() {

src/scroll/index.wc

@@ -391,8 +391,7 @@ export default class Scroll {
       subtree: true,
       attributeFilter: ['style']
     })
-
-    this._initFn(new Event('mounted'))
+    $.nextTick(_ => this._initFn(new Event('mounted')))
   }
 
   unmounted() {