December 2017
Intermediate to advanced
329 pages
6h 9m
Chinese
Content preview from React学习手册
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React
进阶
｜
79
<li class="frown">frown</li>
<li class="frown">frown</li>
<li class="frown">frown</li>
<li class="frown">frown</li>
</ul>
6.
构建和追加第
5
个列表元素：
<ul>
<li class="frown">frown</li>
<li class="frown">frown</li>
<li class="frown">frown</li>
<li class="frown">frown</li>
<li class="frown">frown</li>
</ul>
如果我们通过擦除和重建
DOM
的方式修改
UI
，那么我们需要插入
5
个新的
DOM
元
素。向
DOM
中插入一个元素是代价高昂的
DOM API
操作之一，因为它太慢了。相比
之下，更新已存在的
DOM
元素比插入新元素快得多。
ReactDOM.render
通过保留当前
DOM
，适时更新需要更新的
DOM
元素，来达到更新
UI
的目的。在我们的示例中，只有
3
个元素发生了变化，因此
ReactDOM.render
只需更新
这
3
个
DOM
元素即可（见图
4-5
）。
图
4
-
5
：被更新的
3
个DOM元素
如果需要插入新的
DOM
元素，
ReactDOM
将会插入它们，不过会尝试花最小的代价完
成这些插入操作（最耗资源的操作）。
这种智能化的
DOM
渲染对
React
的高效运作是非常有必要的，因为我们的应用程序的
State
经常会发生变动。每次我们修改了它的 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.