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643 lines
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HTML
643 lines
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HTML
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<a href="/react/tips/dom-event-listeners.html">DOM Event Listeners in a Component</a>
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<a href="/react/tips/initial-ajax.html">Load Initial Data via AJAX</a>
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<a href="/react/tips/false-in-jsx.html">False in JSX</a>
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<a href="/react/tips/communicate-between-components.html">Communicate Between Components</a>
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<a href="/react/tips/expose-component-functions.html">Expose Component Functions</a>
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<a href="/react/tips/children-undefined.html">this.props.children undefined</a>
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<a href="/react/tips/use-react-with-other-libraries.html">Use React with Other Libraries</a>
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<li>
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<a href="/react/tips/dangerously-set-inner-html.html">Dangerously Set innerHTML</a>
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</ul>
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</div>
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</div>
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<div class="inner-content">
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<h1>
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JSX in Profondità
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/02.1-jsx-in-depth.it-IT.md" target="_blank">Edit on GitHub</a>
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</h1>
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<div class="subHeader"></div>
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<p><a href="https://facebook.github.io/jsx/">JSX</a> è un'estensione della sintassi JavaScript che somiglia all'XML. Puoi usare una semplice trasformazione sintattica di JSX con React.</p>
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<h2><a class="anchor" name="perch-jsx"></a>Perché JSX? <a class="hash-link" href="#perch-jsx">#</a></h2>
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<p>Non devi per forza utilizzare JSX con React. Puoi anche usare semplice JS. Tuttavia, raccomandiamo di utilizzare JSX perché usa una sintassi concisa e familiare per definire strutture ad albero dotate di attributi.</p>
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<p>È più familiare a sviluppatori occasionali come i designer.</p>
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<p>L'XML ha i benefici di tag di apertura e chiusura bilanciati. Ciò rende la lettura di grandi strutture ad albero più semplice di chiamate a funzione o oggetti letterali.</p>
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<p>Non altera la semantica di JavaScript.</p>
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<h2><a class="anchor" name="tag-html-o-componenti-react"></a>Tag HTML o Componenti React <a class="hash-link" href="#tag-html-o-componenti-react">#</a></h2>
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<p>React può sia rendere tag HTML (stringhe) che componenti React (classi).</p>
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<p>Per rendere untag HTML, usa nomi di tag minuscoli in JSX:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">myDivElement</span> <span class="o">=</span> <span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"foo"</span> <span class="o">/></span><span class="p">;</span>
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<span class="nx">ReactDOM</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span><span class="nx">myDivElement</span><span class="p">,</span> <span class="nb">document</span><span class="p">.</span><span class="nx">getElementById</span><span class="p">(</span><span class="s1">'example'</span><span class="p">));</span>
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</code></pre></div>
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<p>Per rendere un componente React, definisci una variabile locale che comincia con una lettera maiuscola:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">MyComponent</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span><span class="cm">/*...*/</span><span class="p">});</span>
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<span class="kd">var</span> <span class="nx">myElement</span> <span class="o">=</span> <span class="o"><</span><span class="nx">MyComponent</span> <span class="nx">someProperty</span><span class="o">=</span><span class="p">{</span><span class="kc">true</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
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<span class="nx">ReactDOM</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span><span class="nx">myElement</span><span class="p">,</span> <span class="nb">document</span><span class="p">.</span><span class="nx">getElementById</span><span class="p">(</span><span class="s1">'example'</span><span class="p">));</span>
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</code></pre></div>
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<p>Il JSX di React utilizza la convenzione maiuscolo o minuscolo per distinguere tra classi di componenti locali e tag HTML.</p>
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<blockquote>
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<p>Nota:</p>
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<p>Poiché JSX è JavaScript, gli identificatori come <code>class</code> e <code>for</code> sono sconsigliati
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come nomi di attributi XML. Invece, i componenti DOM React si aspettano nomi di proprietà
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come <code>className</code> e <code>htmlFor</code> rispettivamente.</p>
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</blockquote>
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<h2><a class="anchor" name="la-trasformazione"></a>La Trasformazione <a class="hash-link" href="#la-trasformazione">#</a></h2>
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<p>Il JSX di React viene trasformato da una sintassi XML a JavaScript nativo. Gli elementi XML, gli attributi e i figli sono trasformati in argomenti passati a <code>React.createElement</code>.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Nav</span><span class="p">;</span>
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<span class="c1">// Input (JSX):</span>
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<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Nav</span> <span class="nx">color</span><span class="o">=</span><span class="s2">"blue"</span> <span class="o">/></span><span class="p">;</span>
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<span class="c1">// Output (JS):</span>
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<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Nav</span><span class="p">,</span> <span class="p">{</span><span class="nx">color</span><span class="o">:</span><span class="s2">"blue"</span><span class="p">});</span>
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</code></pre></div>
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<p>Osserva che per utilizzare <code><Nav /></code>, la variabile <code>Nav</code> deve essere visibile.</p>
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<p>JSX permette anche di specificare i figli usando una sintassi XML:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Nav</span><span class="p">,</span> <span class="nx">Profile</span><span class="p">;</span>
|
|
<span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Nav</span> <span class="nx">color</span><span class="o">=</span><span class="s2">"blue"</span><span class="o">><</span><span class="nx">Profile</span><span class="o">></span><span class="nx">click</span><span class="o"><</span><span class="err">/Profile></Nav>;</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span>
|
|
<span class="nx">Nav</span><span class="p">,</span>
|
|
<span class="p">{</span><span class="nx">color</span><span class="o">:</span><span class="s2">"blue"</span><span class="p">},</span>
|
|
<span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Profile</span><span class="p">,</span> <span class="kc">null</span><span class="p">,</span> <span class="s2">"click"</span><span class="p">)</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p>JSX inferirà il <a href="/react/docs/component-specs-it-IT.html#displayname">displayName</a> della classe dall'assegnazione delle variabile, quando il valore di displayName è indefinito:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">Nav</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span> <span class="p">});</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">Nav</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span><span class="nx">displayName</span><span class="o">:</span> <span class="s2">"Nav"</span><span class="p">,</span> <span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>Usa la <a href="https://babeljs.io/repl/">REPL di Babel</a> per provare il JSX e vedere come viene trasformato
|
|
in JavaScript nativo, e il
|
|
<a href="/react/html-jsx.html">convertitore da HTML a JSX</a> per convertire il tuo HTML esistente a
|
|
JSX.</p>
|
|
|
|
<p>Se desideri utilizzare JSX, la guida <a href="/react/docs/getting-started-it-IT.html">Primi Passi</a> ti mostra come impostare la compilazione.</p>
|
|
|
|
<blockquote>
|
|
<p>Nota:</p>
|
|
|
|
<p>L'espressione JSX viene sempre valutata come un ReactElement. Le implementazioni
|
|
attuali potrebbero differire. Un modo ottimizzato potrebbe porre il
|
|
ReactElement in linea come un oggetto letterale per evitare il codice di validazione in
|
|
<code>React.createElement</code>.</p>
|
|
</blockquote>
|
|
<h2><a class="anchor" name="namespace-dei-componenti"></a>Namespace dei Componenti <a class="hash-link" href="#namespace-dei-componenti">#</a></h2>
|
|
<p>Se stai costruendo un componente che ha parecchi figli, come ad esempio un modulo, potresti facilmente trovarti con una quantità di dichiarazioni di variabili:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Imbarazzante blocco di dichiarazioni di variabili</span>
|
|
<span class="kd">var</span> <span class="nx">Form</span> <span class="o">=</span> <span class="nx">MyFormComponent</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">FormRow</span> <span class="o">=</span> <span class="nx">Form</span><span class="p">.</span><span class="nx">Row</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">FormLabel</span> <span class="o">=</span> <span class="nx">Form</span><span class="p">.</span><span class="nx">Label</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">FormInput</span> <span class="o">=</span> <span class="nx">Form</span><span class="p">.</span><span class="nx">Input</span><span class="p">;</span>
|
|
|
|
<span class="kd">var</span> <span class="nx">App</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">FormRow</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">FormLabel</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="nx">FormInput</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="err">/FormRow></span>
|
|
<span class="o"><</span><span class="err">/Form></span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p>Per rendere tutto ciò più semplice e leggibile, <em>i componenti con un namespace</em> ti permettono di usare un componente che dispone di altri componenti come proprietà:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Form</span> <span class="o">=</span> <span class="nx">MyFormComponent</span><span class="p">;</span>
|
|
|
|
<span class="kd">var</span> <span class="nx">App</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Row</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Label</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Input</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="err">/Form.Row></span>
|
|
<span class="o"><</span><span class="err">/Form></span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p>Per fare ciò, devi semplicemente creare i tuoi <em>"sub-componenti"</em> come proprietà del componente principale:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">MyFormComponent</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span> <span class="p">...</span> <span class="p">});</span>
|
|
|
|
<span class="nx">MyFormComponent</span><span class="p">.</span><span class="nx">Row</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span> <span class="p">...</span> <span class="p">});</span>
|
|
<span class="nx">MyFormComponent</span><span class="p">.</span><span class="nx">Label</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span> <span class="p">...</span> <span class="p">});</span>
|
|
<span class="nx">MyFormComponent</span><span class="p">.</span><span class="nx">Input</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span> <span class="p">...</span> <span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>JSX gestirà il tutto correttamente al momento di compilare il tuo codice.</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">App</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">,</span> <span class="kc">null</span><span class="p">,</span>
|
|
<span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Row</span><span class="p">,</span> <span class="kc">null</span><span class="p">,</span>
|
|
<span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Label</span><span class="p">,</span> <span class="kc">null</span><span class="p">),</span>
|
|
<span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Input</span><span class="p">,</span> <span class="kc">null</span><span class="p">)</span>
|
|
<span class="p">)</span>
|
|
<span class="p">)</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<blockquote>
|
|
<p>Nota:</p>
|
|
|
|
<p>Questa funzionalità è disponibile nella <a href="/react/blog/2014/07/17/react-v0.11.html#jsx">v0.11</a> e successive.</p>
|
|
</blockquote>
|
|
<h2><a class="anchor" name="espressioni-javascript"></a>Espressioni JavaScript <a class="hash-link" href="#espressioni-javascript">#</a></h2><h3><a class="anchor" name="expressioni-come-attributi"></a>Expressioni come Attributi <a class="hash-link" href="#expressioni-come-attributi">#</a></h3>
|
|
<p>Per usare un'espressione JavaScript come valore di un attributo, racchiudi l'espressione in un paio
|
|
di parentesi graffe (<code>{}</code>) anziché doppi apici (<code>""</code>).</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">person</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Person</span> <span class="nx">name</span><span class="o">=</span><span class="p">{</span><span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nb">window</span><span class="p">.</span><span class="nx">name</span> <span class="o">:</span> <span class="s1">''</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">person</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span>
|
|
<span class="nx">Person</span><span class="p">,</span>
|
|
<span class="p">{</span><span class="nx">name</span><span class="o">:</span> <span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nb">window</span><span class="p">.</span><span class="nx">name</span> <span class="o">:</span> <span class="s1">''</span><span class="p">}</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div><h3><a class="anchor" name="attributi-booleani"></a>Attributi Booleani <a class="hash-link" href="#attributi-booleani">#</a></h3>
|
|
<p>Omettere il valore di un attributo fa in modo che JSX lo tratti come <code>true</code>. Per passare <code>false</code> occorre utilizzare un'espressione come attributo. Ciò capita spesso quando si usano elementi di moduli HTML, con attributi come <code>disabled</code>, <code>required</code>, <code>checked</code> e <code>readOnly</code>.</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Queste due forme sono equivalenti in JSX per disabilitare un bottone</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="nx">disabled</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="nx">disabled</span><span class="o">=</span><span class="p">{</span><span class="kc">true</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
|
|
<span class="c1">// E queste due forme sono equivalenti in JSX per non disabilitare un bottone</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="nx">disabled</span><span class="o">=</span><span class="p">{</span><span class="kc">false</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
</code></pre></div><h3><a class="anchor" name="expressioni-per-figli"></a>Expressioni per Figli <a class="hash-link" href="#expressioni-per-figli">#</a></h3>
|
|
<p>Similmente, espressioni JavaScript possono essere utilizzate per rappresentare figli:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">content</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Container</span><span class="o">></span><span class="p">{</span><span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="o"><</span><span class="nx">Nav</span> <span class="o">/></span> <span class="o">:</span> <span class="o"><</span><span class="nx">Login</span> <span class="o">/></span><span class="p">}</span><span class="o"><</span><span class="err">/Container>;</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">content</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span>
|
|
<span class="nx">Container</span><span class="p">,</span>
|
|
<span class="kc">null</span><span class="p">,</span>
|
|
<span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Nav</span><span class="p">)</span> <span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Login</span><span class="p">)</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div><h3><a class="anchor" name="commenti"></a>Commenti <a class="hash-link" href="#commenti">#</a></h3>
|
|
<p>È facile aggiungere commenti al tuo codice JSX; sono semplici espressioni JS. Devi soltanto prestare attenzione a porre <code>{}</code> attorno ai commenti quando ti trovi dentro la sezione figli di un tag.</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">content</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">Nav</span><span class="o">></span>
|
|
<span class="p">{</span><span class="cm">/* commento figlio, racchiuso in {} */</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="nx">Person</span>
|
|
<span class="cm">/* commento</span>
|
|
<span class="cm"> su più</span>
|
|
<span class="cm"> righe */</span>
|
|
<span class="nx">name</span><span class="o">=</span><span class="p">{</span><span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nb">window</span><span class="p">.</span><span class="nx">name</span> <span class="o">:</span> <span class="s1">''</span><span class="p">}</span> <span class="c1">// fine del commento su una riga</span>
|
|
<span class="o">/></span>
|
|
<span class="o"><</span><span class="err">/Nav></span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<blockquote>
|
|
<p>NOTA:</p>
|
|
|
|
<p>JSX è simile all'HTML, ma non esattamente identico. Consulta la guida <a href="/react/docs/jsx-gotchas-it-IT.html">JSX gotchas</a> per le differenze fondamentali.</p>
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</blockquote>
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