### Tab
Renders a tabbed menu and view component.

Define a `TabItem` component, pass it to the `Tab` and remove unnecessary nodes expect for `TabItem` by identifying the function's name in `props.children`.
Use the `React.useState()` hook to initialize the value of the `bindIndex` state variable to `props.defaultIndex`. 
Use `Array.prototype.map` on the collected nodes to render the `tab-menu` and `tab-view`. 
Define `changeTab`, which will be executed when clicking a `<button>` from the `tab-menu`.
`changeTab` executes the passed callback, `onTabClick` and updates `bindIndex`, which in turn causes a re-render, evaluating the `style` and `className` of the `tab-view` items and `tab-menu` buttons according to their `index`.

```css
.tab-menu > button {
  cursor: pointer;
  padding: 8px 16px;
  border: 0;
  border-bottom: 2px solid transparent;
  background: none;
}
.tab-menu > button.focus {
  border-bottom: 2px solid #007BEF;
}
.tab-menu > button:hover {
  border-bottom: 2px solid #007BEF;
}
```

```jsx
function TabItem(props) {
  return <div {...props} />;
}

function Tabs(props) {
  const [bindIndex, setBindIndex] = React.useState(props.defaultIndex);
  const changeTab = newIndex => {
    if (typeof props.onTabClick === "function") props.onTabClick(newIndex);
    setBindIndex(newIndex);
  };
  const items = props.children.filter(item => item.type.name === "TabItem");

  return (
    <div className="wrapper">
      <div className="tab-menu">
        {items.map(({ props: { index, label } }) => (
          <button
            onClick={() => changeTab(index)}
            className={bindIndex === index ? "focus" : ""}
          >
            {label}
          </button>
        ))}
      </div>
      <div className="tab-view">
        {items.map(({ props }) => (
          <div
            {...props}
            className="tab-view_item"
            key={props.index}
            style={{ display: bindIndex === props.index ? "block" : "none" }}
          />
        ))}
      </div>
    </div>
  );
}
```
```jsx
ReactDOM.render(
  <Tabs defaultIndex="1" onTabClick={console.log}>
    <TabItem label="A" index="1">
      Lorem ipsum
    </TabItem>
    <TabItem label="B" index="2">
      Dolor sit amet
    </TabItem>
  </Tabs>,
  document.getElementById("root")
);

```

<!-- tags: visual,state,children -->

<!-- expertise: 1 -->