+ add snippet Tabs

snippets/Tabs.md

@@ -0,0 +1,69 @@
+### Tab
+Render a menu and a view, change the content in the view by clicking the button in the menu and the callback will execute before render 
+
+Define the `TabItem` as a middleware, pass it to the `Tab` and remove the useless nodes expect `TabItem` by identify the function's name in `props.children`, after that we will use the collected nodes to render the `tab-menu` and `tab-view` with map. Buttons in the `tab-menu` will execute `changeTab`
+when been clicked, `changeTab` will execute the callback funciton(`onTabClick`) and change `bindIndex` to emit `render`,every node in `tab-view` use `bindIndex` and the `index` which ws passing from `TabItem` to judege whether it show of not(`itemStyle`)
+
+
+```jsx
+class Tab extends React.Component{
+  constructor(props){
+    super(props)
+    this.changeTab(props.defaultIndex)
+    this.state = {
+      bindIndex:''
+    }
+  }
+
+  changeTab(newIndex){
+    if(typeof this.props.onTabClick === 'function'){
+        this.props.onTabClick(newIndex)
+    }
+    this.setState({
+      bindIndex: newIndex
+    })
+  }
+
+  itemStyle(index){
+    return {
+      display:this.state.bindIndex === index?'block':'none'
+    }
+  }
+
+  render(){
+    const items = this.props.children
+                      .filter(item=>item.type.name==='TabItem')
+    return (
+      <div className='wrapper'>
+        <div className='tab-menu'>
+          {items.map(({props:{index, label}})=><button onClick={()=>this.changeTab(index)}>{label}</button>)}
+        </div>
+        <div className='tab-view'>
+          {items.map(({props})=>(
+                     <div {...props}
+                       className='tab-view_item' 
+                       key={props.index} 
+                       style={this.itemStyle(props.index)}/>))}
+        </div>
+      </div>
+    )
+  }
+}
+
+function TabItem(props){
+  return <div {...props}></div>
+}
+```
+```jsx
+ReactDOM.render(
+  <Tab defaultIndex='1' onTabClick={console.log}>
+    <TabItem label='item1' index='1'>item1</TabItem>
+    <TabItem label='item2' index='2'>item2</TabItem>
+  </Tab>,
+  document.getElementById('root')
+);
+```
+
+<!-- tags: visual,children,class -->
+
+<!-- expertise: 1 -->