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182 lines
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HTML
182 lines
10 KiB
HTML
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<li><a href="/react/docs/syntax.html">JSX Syntax</a></li>
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<li><a href="/react/docs/component-basics.html">Component Basics</a></li>
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<li><a href="/react/docs/component-data.html">Component Data</a></li>
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<li><a href="/react/docs/component-lifecycle.html" class="active">Component Lifecycle</a></li>
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<li><a href="/react/docs/event-handling.html">Event Handling</a></li>
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<div class="inner-content">
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<h1>Component Lifecycle</h1>
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<div class="subHeader">What happens when I render a React component?</div>
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<h2>Mounting</h2>
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<p><a href="component-basics.html">We have previously seen</a> how to render components into
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existing DOM elements on the page:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="nx">world</span><span class="o">!<</span><span class="err">/div>, document.body);</span>
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</code></pre></div>
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<p>In this one simple line, we have accomplished the following:</p>
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<ul>
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<li>A <code><div></code> (defined by <code>React.DOM.div</code>) component is instantiated.</li>
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<li>The component is <strong>mounted</strong> into <code>document.body</code>.</li>
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</ul>
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<p><strong>Mounting</strong> is the process of initializing a React component by creating its
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DOM nodes and inserting the them into a supplied container node.</p>
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<p>At this point, the entire page consists of a single <code><div></code> with "Hello,
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world!".</p>
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<h2>Updating</h2>
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<p>Let's add a second call to <code>React.renderComponent()</code> after three
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seconds:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="nx">world</span><span class="o">!<</span><span class="err">/div>, document.body);</span>
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<span class="hll"><span class="nx">setTimeout</span><span class="p">(</span><span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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</span><span class="hll"> <span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="nx">Goodbye</span><span class="p">,</span> <span class="nx">world</span><span class="p">.</span><span class="o"><</span><span class="err">/div>, document.body);</span>
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</span><span class="hll"><span class="p">},</span> <span class="mi">3000</span><span class="p">);</span>
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</span></code></pre></div>
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<p>The second call to <code>React.renderComponent()</code> will trigger the following:</p>
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<ul>
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<li>The <code><div></code> component will check the new props to see if anything changed.</li>
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<li>The set of changes are used to <strong>update</strong> the DOM node as necessary.</li>
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</ul>
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<p><strong>Updating</strong> is the process of mutating the rendered DOM nodes and occurs
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whenever either props or state has changed. This ensures that the rendered DOM
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is consistent with the data.</p>
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<h2>Unmounting</h2>
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<p>Let's add one final call to <code>React.renderComponent()</code> after another three
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seconds:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="nx">world</span><span class="o">!<</span><span class="err">/div>, document.body);</span>
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<span class="nx">setTimeout</span><span class="p">(</span><span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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<span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="nx">Goodbye</span><span class="p">,</span> <span class="nx">world</span><span class="p">.</span><span class="o"><</span><span class="err">/div>, document.body);</span>
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<span class="p">},</span> <span class="mi">3000</span><span class="p">);</span>
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<span class="hll"><span class="nx">setTimeout</span><span class="p">(</span><span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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</span><span class="hll"> <span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span><span class="o"><</span><span class="nx">img</span> <span class="nx">src</span><span class="o">=</span><span class="s2">"/images/fin.png"</span> <span class="o">/></span><span class="p">,</span> <span class="nb">document</span><span class="p">.</span><span class="nx">body</span><span class="p">);</span>
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</span><span class="hll"><span class="p">},</span> <span class="mi">6000</span><span class="p">);</span>
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</span></code></pre></div>
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<p>The third call to <code>React.renderComponent()</code> will trigger the following:</p>
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<ul>
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<li>An <code><img></code> (defined by <code>React.DOM.img</code>) component is instantiated.</li>
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<li>React will compare the <code><div></code> component with the <code><img></code> component.</li>
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<li>Since the component class is different, the <code><div></code> component will be
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<strong>unmounted</strong>.</li>
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<li>The <code><img></code> component will then be mounted into <code>document.body</code>.</li>
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</ul>
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<p><strong>Unmounting</strong> is the process of releasing resources that have been allocated by
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a component. This allows user interfaces built with React to live long without
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memory leaks.</p>
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<p>Components can also be unmounted using
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<code>React.unmountAndReleaseReactRootNode()</code>:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="nx">React</span><span class="p">.</span><span class="nx">unmountAndReleaseReactRootNode</span><span class="p">(</span><span class="nb">document</span><span class="p">.</span><span class="nx">body</span><span class="p">);</span>
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</code></pre></div>
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<p>This will unmount any components mounted immediately within <code>document.body</code>.</p>
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