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<h1 id="The-Road-to-learn-React书籍学习笔记-第二章"><a href="#The-Road-to-learn-React书籍学习笔记-第二章" class="headerlink" title="The Road to learn React书籍学习笔记(第二章)"></a>The Road to learn React书籍学习笔记(第二章)</h1><h2 id="组件的内部状态"><a href="#组件的内部状态" class="headerlink" title="组件的内部状态"></a>组件的内部状态</h2><p>组件的内部状态也称为局部状态，允许保存、修改和删除在组件内部的属性，使用ES6类组件可以在构造函数中初始化组件的状态。构造函数只会在组件初始化的时候调用一次</p>
<p>类构造函数</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">class App extends Component{</span><br><span class="line"> constructor(props){</span><br><span class="line"> super(props);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>使用ES6编写的组件有一个构造函数时，需要强制地使用 <code>super()</code> 方法， 因为这个 <code>App组件</code> 是 <code>Component</code> 的子类，因为需要在 <code>App组件</code> 声明 <code>extends Component</code><br>也可以调用 <code>super(props)</code>，它会在构造函数中设置 <code>this.props</code> 以供构造函数中访问。否则在构造函数中访问 <code>this.props</code> ，会得到 <code>undefined</code></p>
<p>例子，组件的初始状态是一个列表</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line">const list = [</span><br><span class="line"> {</span><br><span class="line"> title:'React',</span><br><span class="line"> url: 'https://facebook.github.io/react/',</span><br><span class="line"> author: 'Jordan Walke',</span><br><span class="line"> num_comments: 3,</span><br><span class="line"> points: 4,</span><br><span class="line"> objectID: 0,</span><br><span class="line"> }</span><br><span class="line">];</span><br><span class="line"></span><br><span class="line">class App extends Component{</span><br><span class="line"> constructor(props){</span><br><span class="line"> super(props);</span><br><span class="line"> this.state = {</span><br><span class="line"> list : list,</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>state</code> 通过使用 <code>this</code> 绑定在类上，因此可以在整个组件中访问到 <code>state</code>。通过 <code>render()</code> 方法可以映射一个在组件外定义静态列表</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line">class App extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> return(</span><br><span class="line"> <div className = "App"></span><br><span class="line"> {this.state.list.map(item =></span><br><span class="line"> <div key = {item.objectID}></span><br><span class="line"> <span><a href = {item.url}>{item.title}</a></span></span><br><span class="line"> <span>{item.author}</span></span><br><span class="line"> <span>{item.num_comments}</span></span><br><span class="line"> <span>{item.points}</span></span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line"> </div></span><br><span class="line"> );</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>现在list是㢟的一部分，它在组件的 <code>state</code> 中，可以从list添加、修改、删除列表项。组件的 <code>render</code> 会再次运行，可以简单修改组件内部状态，确保组件重新渲染并且展示从内部状态获取到的正确数据<br>修改 <code>state</code> 可以使用 <code>setState()</code> 方法来修改 </p>
<h2 id="ES6-对象初始化"><a href="#ES6-对象初始化" class="headerlink" title="ES6 对象初始化"></a>ES6 对象初始化</h2><p>初始化例子</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">const name = 'Laibh';</span><br><span class="line">const user = {</span><br><span class="line"> name ： name</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<p>当对象中属性名与变量名相同时可以如下操作</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">const name = 'Laibh'; </span><br><span class="line">const user = {</span><br><span class="line"> name</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<p>在应用程序中，列表变量名与状态属性名称共享同一名称</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">//ES5 </span><br><span class="line">this.state = {</span><br><span class="line"> list:list</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">//ES6</span><br><span class="line">this.state = {</span><br><span class="line"> list</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<p>简写方法名</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">//ES5</span><br><span class="line">var userService = {</span><br><span class="line"> getUserName :function(user){</span><br><span class="line"> return user.firstname + ' ' + user.lastname;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">//ES6</span><br><span class="line">const userService = {</span><br><span class="line"> getUserName(user){</span><br><span class="line"> return user.firstname + ' ' + user.lastname;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>计算属性名</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">//ES5</span><br><span class="line">var user = {</span><br><span class="line"> name:'Laibh'</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">//ES6</span><br><span class="line">const key = 'name';</span><br><span class="line">const user = {</span><br><span class="line"> [key] :'Laibh'</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="单向数据流"><a href="#单向数据流" class="headerlink" title="单向数据流"></a>单向数据流</h2><p>组件中有一些内部的 <code>state</code>，练习 <code>state</code> 操作的好方式增加一些组件的互动<br>为列表增加一个删除按钮</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line"> class App extends Component {</span><br><span class="line"></span><br><span class="line"> render() {</span><br><span class="line"> return (</span><br><span class="line"> <div className="App"></span><br><span class="line"> {this.state.list.map(item =></span><br><span class="line"> <div key={item.objectID}></span><br><span class="line"> <span></span><br><span class="line"> <a href={item.url}>{item.title}</a></span><br><span class="line"> </span></span><br><span class="line"> <span>{item.author}</span></span><br><span class="line"> <span>{item.num_comments}</span></span><br><span class="line"> <span>{item.points}</span></span><br><span class="line"> <span></span><br><span class="line"> <button</span><br><span class="line"> onClick={() => this.onDismiss(item.objectID)}</span><br><span class="line"> type="button"</span><br><span class="line"> ></span><br><span class="line"> Dismiss</span><br><span class="line"> </button></span><br><span class="line"> </span></span><br><span class="line"> </div></span><br><span class="line"> )}</span><br><span class="line"> </div></span><br><span class="line"> );</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>上面类中，<code>onDismiss()</code> 还没有被定义，它通过id来标识哪个应该被删除，此函数绑定到类，就成为了类方法，所以访问它的时候要用 <code>this.onDismiss()</code> 而不是用 <code>onDismiss()</code> 。<code>this</code> 对象是类的实例，为了将 <code>onDismiss()</code> 定义为类方法，需要在构造函数中绑定它。并定义它的逻辑功能</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"> class App extends Component {</span><br><span class="line"></span><br><span class="line"> constructor(props) {</span><br><span class="line"> super(props);</span><br><span class="line"></span><br><span class="line"> this.state = {</span><br><span class="line"> list,</span><br><span class="line"> };</span><br><span class="line"></span><br><span class="line"> this.onDismiss = this.onDismiss.bind(this);</span><br><span class="line"> }</span><br><span class="line"> onDismiss(id) {</span><br><span class="line"> ...</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> render() {</span><br><span class="line"> ...</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>可以使用JavaScript内置的 <code>filter</code> 方法来删除列表的一项，它会遍历整个列表，通过条件来过滤，匹配的返回 <code>true</code> 并留在列表中</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">onDismiss(id){</span><br><span class="line"> const updateList = this.state.list.filter(function isNotId(item){</span><br><span class="line"> return item.objectID !== id</span><br><span class="line"> });</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>或者一行箭头函数</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">onDismiss(id){</span><br><span class="line"> const updateList = this.state.list.filter(item => item.objectID !== id);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>接着要更新数据</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">this.setState({list:updateList});</span><br></pre></td></tr></table></figure>
<h2 id="绑定"><a href="#绑定" class="headerlink" title="绑定"></a>绑定</h2><p>类不会自动绑定 <code>this</code> 到实例上<br>需要自己绑定</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">constructor() {</span><br><span class="line"> super();</span><br><span class="line"></span><br><span class="line"> this.onClickMe = this.onClickMe.bind(this);</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
<p>类的绑定方法也有人写在其他地方，例如render()函数中</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">render(){</span><br><span class="line"> return(</span><br><span class="line"> <button onClick = {this.onClickMe.bind(this)}>Click Me</button></span><br><span class="line"> )</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>但是应该避免这样使用，因为它会在每次 <code>render()</code> 方法执行的时绑定类方法。组件每次更新都会导致性能消耗，当在构造函数中绑定的时候，绑定只会在组件实例化时运行一次，这样是一个更好的方式</p>
<p>另外有一些人剔除在构造函数中定义业务逻辑类方法</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">constructor(){</span><br><span class="line"> super();</span><br><span class="line"> this.onClick = () =>{</span><br><span class="line"> conlose.log(this);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>这样随着时间推移会让构造函数变得混乱，避免使用。构造函数的目的只是实例化类以及所有的属性</p>
<h2 id="事件处理"><a href="#事件处理" class="headerlink" title="事件处理"></a>事件处理</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><button</span><br><span class="line"> onClick={() => this.onDismiss(item.objectID)}</span><br><span class="line"> type="button"></span><br><span class="line"> Dismiss</span><br><span class="line"></button></span><br></pre></td></tr></table></figure>
<p>当传递一个参数到类的方法，需要将它封装到另一个（箭头）函数中，由于要传递给事件处理器使用，因为它必须是一个函数，而下面的这个代码不会工作。因为类方法会在浏览器中打开程序时候立即执行</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><button onClick = {this.onDismiss(item.objectID)}></span><br><span class="line"> Dismiss</span><br><span class="line"></button></span><br></pre></td></tr></table></figure>
<p>倘若写成 </p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><button onClick = {onDismiss}></span><br><span class="line"> Dismiss</span><br><span class="line"></button></span><br></pre></td></tr></table></figure>
<p>就不会立即执行，但是需要传参数，所以就不这么用</p>
<p>另外的一个解决方案是在外部定义一个包装函数，并且只将定义的函数传递给处理程序。因为需要访问特定的列表项，所以它必须位于 <code>map</code> 函数块的内部</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line">class App extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> return(</span><br><span class="line"> <div className = "App"></span><br><span class="line"> {this.state.list.map(item =></span><br><span class="line"> const onHandldDismiss = () =></span><br><span class="line"> this.onDismiss(item.objectID);</span><br><span class="line"></span><br><span class="line"> return(</span><br><span class="line"> <div key={item.objectID}></span><br><span class="line"> <span></span><br><span class="line"> <a href={item.url}>{item.title}</a></span><br><span class="line"> </span></span><br><span class="line"> <span>{item.author}</span></span><br><span class="line"> <span>{item.num_comments}</span></span><br><span class="line"> <span>{item.points}</span></span><br><span class="line"> <span></span><br><span class="line"> <button</span><br><span class="line"> onClick={onHandleDismiss}</span><br><span class="line"> type="button"</span><br><span class="line"> ></span><br><span class="line"> Dismiss</span><br><span class="line"> </button></span><br><span class="line"> </span></span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> )}</span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>在事件处理程序中使用箭头函数对性能会有影响</p>
<h2 id="和表单互动"><a href="#和表单互动" class="headerlink" title="和表单互动"></a>和表单互动</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">const list = [{</span><br><span class="line"> title: 'React',</span><br><span class="line"> url: 'https://facebook.github.io/react',</span><br><span class="line"> author: 'Jordan Walke',</span><br><span class="line"> num_comments: 3,</span><br><span class="line"> points: 4,</span><br><span class="line"> objectID: 0,</span><br><span class="line">}, {</span><br><span class="line"> title: 'Redux',</span><br><span class="line"> url: 'https://github.com/reactjs/redux',</span><br><span class="line"> author: 'Dan Abramov, Andrew Clark',</span><br><span class="line"> num_comments: 2,</span><br><span class="line"> points: 5,</span><br><span class="line"> objectID: 1, </span><br><span class="line">}];</span><br></pre></td></tr></table></figure>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br></pre></td><td class="code"><pre><span class="line">const isSearched = searchText => item => item.title.toLowerCase().includes(searchText.toLowerCase());</span><br><span class="line">class FormP extends Component{</span><br><span class="line"> constructor(props){</span><br><span class="line"> super(props);</span><br><span class="line"> this.state = {list,searchText:''};</span><br><span class="line"> this.onSearchChange = this.onSearchChange.bind(this);</span><br><span class="line"> this.onDismiss = this.onDismiss.bind(this);</span><br><span class="line"> }</span><br><span class="line"> onSearchChange(e){</span><br><span class="line"> this.setState({searchText:e.target.value});</span><br><span class="line"> }</span><br><span class="line"> onDismiss(id){</span><br><span class="line"> console.log(this);</span><br><span class="line"> const updateList = this.state.list.filter(item =></span><br><span class="line"> item.objectID !== id</span><br><span class="line"> );</span><br><span class="line"> this.setState({list:updateList});</span><br><span class="line"> }</span><br><span class="line"> render(){</span><br><span class="line"> return(</span><br><span class="line"> <div className = "FormP"></span><br><span class="line"> <form></span><br><span class="line"> <input type="text" onChange = {this.onSearchChange}/></span><br><span class="line"> </form></span><br><span class="line"> {this.state.list.filter(isSearched(this.state.searchText)).map(</span><br><span class="line"> item =></span><br><span class="line"> <div key = {item.objectID}></span><br><span class="line"> <span></span><br><span class="line"> <a href= {item.url}>{item.title}</a></span><br><span class="line"> </span></span><br><span class="line"> <span>{item.author}</span></span><br><span class="line"> <span>{item.num_comments}</span></span><br><span class="line"> <span>{item.points}</span></span><br><span class="line"> <span></span><br><span class="line"> <button onClick = {()=>this.onDismiss(item.objectID)}>Dismiss</button></span><br><span class="line"> </span></span><br><span class="line"> </div> </span><br><span class="line"> )}</span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">export default FormP;</span><br></pre></td></tr></table></figure>
<h2 id="ES6-解构"><a href="#ES6-解构" class="headerlink" title="ES6 解构 "></a>ES6 解构 </h2><p>在JavaScript ES6 中有一个更方便的方法来访问对象和数组的属性，叫做解构。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line">const user = {</span><br><span class="line"> firsname : 'L',</span><br><span class="line"> lastname : 'binhong'</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">//ES5</span><br><span class="line">var firstname = user.firstname;</span><br><span class="line">var lastname = user.lastname;</span><br><span class="line"></span><br><span class="line">console.log(firstname + '' +lastname);</span><br><span class="line"></span><br><span class="line">//ES6</span><br><span class="line">const {firstname, lastname} = user;</span><br><span class="line">conlose.log(firstname + '' +lastname);</span><br></pre></td></tr></table></figure>
<p>在JavaScript ES5中每次访问对象的属性都需要额外添加一行代码，但是ES6中就可以在一行中进行，可读性最好的方法就是将对象解构成多个属性时使用多行<br>对于数组也可以使用解构，可以保持代码的可读性</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">const user = ['1','2','3'];</span><br><span class="line">const [</span><br><span class="line"> a,</span><br><span class="line"> b,</span><br><span class="line"> c</span><br><span class="line">] = user;</span><br><span class="line"></span><br><span class="line">console.log(a,b,c); //1,2,3</span><br></pre></td></tr></table></figure>
<h2 id="受控组件"><a href="#受控组件" class="headerlink" title="受控组件"></a>受控组件</h2><p>表单元素 <code><input></code>/<code><select></code>/<code><textarea></code> 会以元素HTML的形式保存它们自己的状态，一旦有人从外部做了修改，就会修改内部的值，在React中这被称为不受控组件，因为它们自己处理状态，在React中，我们得把它们变成 <strong>受控元素</strong></p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">class App extends Componet{</span><br><span class="line"> render(){</span><br><span class="line"> const {searchText,list} = this.state;</span><br><span class="line"> return(</span><br><span class="line"> <div className = "App"></span><br><span class="line"> <form></span><br><span class="line"> <input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {searchText}</span><br><span class="line"> onChange = {this.onSearchChange}</span><br><span class="line"> ></input></span><br><span class="line"> </form></span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>现在输入框的单项数据流循环是自包含的，组件内部状态是输入框的唯一数据来源</p>
<h2 id="拆分组件"><a href="#拆分组件" class="headerlink" title="拆分组件"></a>拆分组件</h2><p>用于搜索的输入组件和一个用于展示的列表组件</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">class App extends Componet{</span><br><span class="line"> render(){</span><br><span class="line"> const {searchText,list} = this.state;</span><br><span class="line"> return(</span><br><span class="line"> <div className = "App"></span><br><span class="line"> <Search /></span><br><span class="line"> <Table /></span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>在组件传递属性并在组件中使用，App组件需要传递本地状态 <code>state</code> 托管的属性和它自己的类方法</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">class App extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> const {searchText,list} = this.state;</span><br><span class="line"> return(</span><br><span class="line"> <div></span><br><span class="line"> <Search </span><br><span class="line"> value = {searchText}</span><br><span class="line"> onChange = {this.onSearchChange} /></span><br><span class="line"> <Table </span><br><span class="line"> list = {list}</span><br><span class="line"> pattern = {searchText}</span><br><span class="line"> onDismiss = {this.onDismiss} /></span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>Search组件</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">class Search extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> const {value,onChange} = this.props;</span><br><span class="line"> return(</span><br><span class="line"> <form></span><br><span class="line"> <input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {value}</span><br><span class="line"> onChange = {onChange} /></span><br><span class="line"> </form></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>Table组件</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line">class Table extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> const {list,pattern.onDismiss} = this.props;</span><br><span class="line"> return(</span><br><span class="line"> <div></span><br><span class="line"> {list.filter(isSearched(pattern)).map(item =></span><br><span class="line"> <div key = {item.objectID}></span><br><span class="line"> <span><a href = {item.url}>{item.title}</a></span></span><br><span class="line"> <span>{item.title}</span></span><br><span class="line"> <soan>{item.points}</span></span><br><span class="line"> <span>{item.num_comments}</span></span><br><span class="line"> <button onClick ={() => onDismiss(item.objectID)}></span><br><span class="line"> Dismiss</span><br><span class="line"> </button></span><br><span class="line"> </div></span><br><span class="line"> )}</span><br><span class="line"> </div></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="可组合组件"><a href="#可组合组件" class="headerlink" title="可组合组件"></a>可组合组件</h2><p>在 <code>props</code> 对象中还有一个小小的属性可以供使用： <code>children</code> 属性.通过这个属性可以将元素从上层传递到组件中，这些元素对组件来说是未知的，但是却为组件互相结合提供了可能性、<br>下例中，将一个文本作为子元素传递到Search组件中</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">class App extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> const {searchText,list} = user;</span><br><span class="line"> return(</span><br><span class="line"> <div></span><br><span class="line"> <Search </span><br><span class="line"> value = {searchText}</span><br><span class="line"> onChange = {this.onSearchChange} /></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>在 <code>Search</code> 组件可以从 <code>props</code> 对象中解构出 <code>children</code> 属性，就可以指定它应该在哪里显示</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">class Search extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> const {value,onChange,children} = this.props;</span><br><span class="line"> return(</span><br><span class="line"> <form></span><br><span class="line"> {children}</span><br><span class="line"> <input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {value}</span><br><span class="line"> onChange = {onChange} /></span><br><span class="line"> }</span><br><span class="line"> </form></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="可复用组件"><a href="#可复用组件" class="headerlink" title="可复用组件"></a>可复用组件</h2><p>可复用和可组合组件帮助理解合理的组件分层，它们是React视图层的基础</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">class Button extends Component{</span><br><span class="line"> render(){</span><br><span class="line"> const {onClick,className,children} = this.props;</span><br><span class="line"> return(</span><br><span class="line"> <button </span><br><span class="line"> onClick = {onClick}</span><br><span class="line"> className = {className}</span><br><span class="line"> type = "button"></span><br><span class="line"> {children}</span><br><span class="line"> </button></span><br><span class="line"> )</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>Button组件拥有单一可信数据源，一个Button组件可以立即重构所有button。一个Button组件统治了所有button</p>
<blockquote>
<p><code><Button onclick = {() => onDismiss(item.objectID)}>Dissmiss</Button></code></p>
</blockquote>
<h2 id="函数式无状态组件-function-stateless-componenet"><a href="#函数式无状态组件-function-stateless-componenet" class="headerlink" title="函数式无状态组件(function stateless componenet)"></a>函数式无状态组件(function stateless componenet)</h2><p>这类组件就是函数，它们接受一个输入并返回一个输出。输入时props，输出就是一个普通的JSX组件实例。函数式无状态组件是函数，并且它们没有本地状态。不能通过 <code>this.state</code> 或者是 <code>this.setState()</code> 来访问或者更新状态，因为这里没有 <code>this</code> 对象，此外，它也没有生命周期方法。 <code>constructor()</code> 与 <code>render()</code> 就是其中两个。 <code>constructor</code> 在一个组件的生命周期只执行一次，而 <code>render()</code> 方法只会在最开始执行一次</p>
<h3 id="ES6-类组件"><a href="#ES6-类组件" class="headerlink" title="ES6 类组件"></a>ES6 类组件</h3><p>在类的定义中，它们继承自 <code>React</code> 组件。 <code>extend</code> 会注册所有的生命周期方法，只要在 <code>React component API</code>中，都可以在组件中使用。通过这种方式，可以使用 <code>render()</code> 方法，此外还可以通过使用 <code>this.state</code> 和 <code>this.setState()</code> 来存储和操作 <code>state</code></p>
<p>把上例的Search组件重构为一个函数式无状态组件</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">function Search(props){</span><br><span class="line"> const {value,onChange,children} = props;</span><br><span class="line"> return{</span><br><span class="line"> <form></span><br><span class="line"> {children}<input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {value}</span><br><span class="line"> onChange = {onChange} /></span><br><span class="line"> </form></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>或者将参数放在函数里面</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">function Search({value,onChange,children}){</span><br><span class="line"> return{</span><br><span class="line"> <form></span><br><span class="line"> {children}<input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {value}</span><br><span class="line"> onChange = {onChange} /></span><br><span class="line"> </form></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>然后ES6 箭头函数一波</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">const Search = ({value,onChange,children}) =></span><br><span class="line"> <form></span><br><span class="line"> {children}<input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {value}</span><br><span class="line"> onChange = {onChange} /></span><br><span class="line"> </form></span><br></pre></td></tr></table></figure>
<p>如果想在ES6箭头函数写法中做些事情的话 可以这样写</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line">const Search = ({value,onChange,children}) => {</span><br><span class="line"></span><br><span class="line"> //do something</span><br><span class="line"> return(</span><br><span class="line"> <form></span><br><span class="line"> {children}<input</span><br><span class="line"> type = "text"</span><br><span class="line"> value = {value}</span><br><span class="line"> onChange = {onChange} /></span><br><span class="line"> </form></span><br><span class="line"> )</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="给组件声明样式"><a href="#给组件声明样式" class="headerlink" title="给组件声明样式"></a>给组件声明样式</h2><p>可以复用 <code>src/App.css</code> 或者 <code>src/index.css</code> 文件</p>
<p>参考链接：<a href="https://leanpub.com/the-road-to-learn-react-chinese">https://leanpub.com/the-road-to-learn-react-chinese</a></p>
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<div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#The-Road-to-learn-React书籍学习笔记-第二章"><span class="nav-number">1.</span> <span class="nav-text">The Road to learn React书籍学习笔记(第二章)</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#组件的内部状态"><span class="nav-number">1.1.</span> <span class="nav-text">组件的内部状态</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#ES6-对象初始化"><span class="nav-number">1.2.</span> <span class="nav-text">ES6 对象初始化</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#单向数据流"><span class="nav-number">1.3.</span> <span class="nav-text">单向数据流</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#绑定"><span class="nav-number">1.4.</span> <span class="nav-text">绑定</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#事件处理"><span class="nav-number">1.5.</span> <span class="nav-text">事件处理</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#和表单互动"><span class="nav-number">1.6.</span> <span class="nav-text">和表单互动</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#ES6-解构"><span class="nav-number">1.7.</span> <span class="nav-text">ES6 解构 </span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#受控组件"><span class="nav-number">1.8.</span> <span class="nav-text">受控组件</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#拆分组件"><span class="nav-number">1.9.</span> <span class="nav-text">拆分组件</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#可组合组件"><span class="nav-number">1.10.</span> <span class="nav-text">可组合组件</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#可复用组件"><span class="nav-number">1.11.</span> <span class="nav-text">可复用组件</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#函数式无状态组件-function-stateless-componenet"><span class="nav-number">1.12.</span> <span class="nav-text">函数式无状态组件(function stateless componenet)</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#ES6-类组件"><span class="nav-number">1.12.1.</span> <span class="nav-text">ES6 类组件</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#给组件声明样式"><span class="nav-number">1.13.</span> <span class="nav-text">给组件声明样式</span></a></li></ol></li></ol></div>
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