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The Diffing Algorithm: Keys
//now React knows that the element with key '2014' is the new one,
//and the elements with the keys '2015' and '2016' have just moved.
<ul>
<li key="2015">Duke</li>
<li key="2016">Villanova</li>
</ul>
<ul>
<li key="2014">Connecticut</li>
<li key="2015">Duke</li>
<li key="2016">Villanova</li>
</ul>When children have keys, React uses the key to match children in the original tree with children in the subsequent tree.