优化markd组件

src/markd/index.wc

@@ -209,6 +209,7 @@ export default class Markd {
     } else {
       this.__BOX__.innerHTML = ''
     }
+    this.removeAttribute('md')
   }
 
   clear() {
@@ -241,5 +242,15 @@ export default class Markd {
     this.__observer.disconnect()
     this.clear()
   }
+
+  watch() {
+    switch (name) {
+      case 'md':
+        if (val !== null) {
+          this.md = val
+        }
+        break
+    }
+  }
 }
 </script>