React添加到模板？

Question

      var arr = [
        <h1>Hello world!</h1>,
        <h2>React is awesome</h2>,
      ];
      ReactDOM.render(
        <div>{arr}</div>,
        document.getElementById('example3')
      );

这段代码执行的时候警告

Warning: Each child in an array or iterator should have a unique "key" prop. Check the top-level render call using <div>. See https://fb.me/react-warning-keys for more information.

我查了一下意思就是最好给循环产生的child添加一个key，

这段代码怎么加key，不加key就出现警告

Answer 1

 var arr = [
    <h1 key="h1">Hello world!</h1>,
    <h2 key="h2">React is awesome</h2>,
  ];
  ReactDOM.render(
    <div>{arr}</div>,
    document.getElementById('example3')
  );