3.3 React Only Updates What's Necessary React只会进行必要的更新

React DOM compares the element and its children to the previous one,

React DOM将元素及其子元素与前一个元素进行比较，

and only applies the DOM updates necessary to bring the DOM to the desired state.

并且仅对状态为需要更新的DOM进行DOM更新。

You can verify by inspecting the last example with the browser tools:

你可以通过浏览器工具对最后一个事例进行验证检验：

图片发自App

Even though we create an element describing the whole UI tree on every tick, only the text node whose contents has changed gets updated by React DOM.

即使我们不断的创建一个元素描述整个UI，但是也只有文本节点的内容的改动被React DOM更新了。