diff --git a/js-framework/demo.ts b/js-framework/demo.ts
index 1fe4c7d2..47318bf1 100644
--- a/js-framework/demo.ts
+++ b/js-framework/demo.ts
@@ -100,9 +100,14 @@ enum State {
 class SnakeModel {
     state = State.idel
     direction = Direction.left
-    width = 10
-    height = 10
 
+    width: number
+    height: number
+
+    constructor(w: number, h: number) {
+        this.width = w
+        this.height = h
+    }
     food = { x: 0, y: 0 }
 
     head: SnakeNode = {
@@ -192,6 +197,7 @@ class SnakeModel {
 }
 
 class SnakeView extends ViewHolder {
+    panel: Stack = new Stack
 
     build(root: Group): void {
         root.bgColor = Color.parse('#000000')
@@ -205,23 +211,66 @@ class SnakeView extends ViewHolder {
                 top: 20
             }
         } as StackConfig
+        root.addChild(this.panel)
         root.addChild(title)
     }
 }
 
 class SnakeVM extends ViewModel<SnakeModel, SnakeView>{
-    binding(v: SnakeView, model: SnakeModel) {
+    timerId?: any
 
+    start() {
+        if (this.timerId !== undefined) {
+            clearInterval(this.timerId)
+        }
+        this.timerId = setInterval(() => {
+            this.getModel().step()
+        }, 1000)
+    }
+
+    stop() {
+        if (this.timerId !== undefined) {
+            clearInterval(this.timerId)
+            this.timerId = undefined
+        }
+    }
+
+    binding(v: SnakeView, model: SnakeModel) {
+        v.panel.width = model.width * 10
+        v.panel.height = model.height * 10
+        let node: SnakeNode | undefined = model.head
+        let nodes: SnakeNode[] = []
+        while (node != undefined) {
+            nodes.push(node)
+            node = node.next
+        }
+        nodes.forEach((e, index) => {
+            let item = v.panel.children[index]
+            if (item) {
+                item.x = e.x * 10
+                item.height = e.y * 10
+            } else {
+                item = new Stack
+                item.bgColor = Color.parse('#0000ff')
+                item.width = item.height = 10
+                v.panel.addChild(item)
+            }
+        })
+        if (nodes.length < v.panel.children.length) {
+            v.panel.children.length = nodes.length
+        }
     }
 }
 
 @Entry
 class SnakePanel extends VMPanel<SnakeModel, SnakeView>{
+
     getVMClass() {
         return SnakeVM
     }
+
     getModel() {
-        return new SnakeModel
+        return new SnakeModel(this.getRootView().width / 10, this.getRootView().width / 10)
     }
 
     getViewHolder() {
diff --git a/js-framework/src/ui/view.ts b/js-framework/src/ui/view.ts
index af7ffc48..0466eb06 100644
--- a/js-framework/src/ui/view.ts
+++ b/js-framework/src/ui/view.ts
@@ -69,7 +69,7 @@ export abstract class View implements Modeling {
             set: (target, p, v, receiver) => {
                 const oldV = Reflect.get(target, p, receiver)
                 const ret = Reflect.set(target, p, v, receiver)
-                if (Reflect.getMetadata(p, target)) {
+                if (Reflect.getMetadata(p, target) && oldV !== v) {
                     receiver.onPropertyChanged(p.toString(), oldV, v)
                 }
                 return ret
@@ -209,7 +209,7 @@ export interface LinearConfig extends Config {
 export abstract class Group extends View {
 
     @Property
-    children: View[] = new Proxy([], {
+    readonly children: View[] = new Proxy([], {
         set: (target, index, value) => {
             if (index === 'length') {
                 this.getDirtyChildrenModel().length = value as number
@@ -231,6 +231,7 @@ export abstract class Group extends View {
     addChild(view: View) {
         this.children.push(view)
     }
+
     clean() {
         this.children.forEach(e => { e.clean() })
         super.clean()
diff --git a/js-framework/src/vm/mvvm.ts b/js-framework/src/vm/mvvm.ts
index d0e2f2e2..78eea0ce 100644
--- a/js-framework/src/vm/mvvm.ts
+++ b/js-framework/src/vm/mvvm.ts
@@ -30,7 +30,7 @@ export abstract class ViewHolder {
 
 export abstract class VMPanel<M extends Object, V extends ViewHolder> extends Panel {
 
-    private vm: ViewModel<M, V> = new (this.getVMClass())(this.getModel(), this.getViewHolder())
+    private vm?: ViewModel<M, V>
 
     abstract getVMClass(): new (m: M, v: V) => ViewModel<M, V>
 
@@ -44,6 +44,7 @@ export abstract class VMPanel<M extends Object, V extends ViewHolder> extends Pa
     }
 
     build(root: Group): void {
+        this.vm = new (this.getVMClass())(this.getModel(), this.getViewHolder())
         this.vm.build(root)
     }
 }