path: root/files/it/conflicting/learn/javascript/objects/index.html

---
title: Introduzione a JavaScript Object-Oriented
slug: Web/JavaScript/Introduzione_al_carattere_Object-Oriented_di_JavaScript
tags:
  - Classe
  - Costruttore
  - Eredità
  - Incapsulamento
  - Membri
  - Oggetto
  - Orientato agli oggetti
translation_of: Learn/JavaScript/Objects
translation_of_original: Web/JavaScript/Introduction_to_Object-Oriented_JavaScript
---
<p>{{jsSidebar("Introductory")}}</p>

<p>Orientato agli oggetti fino dal nucleo, JavaScript offre funzionalità {{Glossary("OOP")}} potenti e flessibili. <span id="result_box" lang="it"><span class="hps">Questo</span> <span class="hps">articolo inizia</span> <span class="hps">con una introduzione</span> <span class="hps">alla</span> <span class="hps">programmazione</span> <span class="hps">orientata agli oggetti</span><span>,</span> quindi presenta <span class="hps">il</span> <span class="hps">modello di oggetti</span> <span class="hps">JavaScript</span> <span class="hps">e, infine,</span> <span class="hps">dimostra</span> <span class="hps">concetti della</span> <span class="hps">programmazione orientata agli oggetti</span> <span class="hps">in JavaScript</span><span>.</span></span></p>

<h2 id="JavaScript_Review" name="JavaScript_Review">Riesame su JavaScript</h2>

<p><span id="result_box" lang="it"><span class="hps">Se</span> <span class="hps">non ti senti</span> <span class="hps">sicuro su</span> <span class="hps">concetti</span> <span class="hps">JavaScript</span><span> come</span> <span class="hps">variabili, tipi</span><span>, funzioni e</span> <span class="hps">ambito di applicazione</span><span>,</span> <span class="hps">puoi leggere su</span> <span class="hps">questi argomenti</span> </span>in <a href="/it/JavaScript/Una_re-introduzione_a_JavaScript" title="it/JavaScript/Una_re-introduzione_a_JavaScript">A re-introduction to JavaScript</a>. Puoi<span lang="it"><span class="hps"> inoltre consultare</span> <span class="hps">la</span></span> <a href="/it/JavaScript/Guida" title="it/JavaScript/Guida">Core JavaScript 1.5 Guide</a>.</p>

<h2 id="Object-oriented_programming" name="Object-oriented_programming">Programmazione object-oriented</h2>

<p>La programmazione orientata agli oggetti è un paradigma di programmazione che usa astrazione ({{glossary("abstraction")}}) per creare modelli basati sul mondo reale. Utilizza diverse tecniche di paradigmi esistenti, tra cui la modularità ({{glossary("modularity")}}), il polimorfismo ({{glossary("polymorphism")}}) e l'incapsulamento ({{glossary("encapsulation")}}). Oggi molti linguaggi di programmazione (come Java, JavaScript, C #, C ++, Python, PHP, Ruby e Objective-C) supportano la programmazione orientata agli oggetti (OOP).</p>

<p><span id="result_box" lang="it">OOP <span class="hps">ha una visione del</span> <span class="hps">software come</span> <span class="hps">un insieme di oggetti</span> <span class="hps">cooperanti</span><span>,</span> <span class="hps">piuttosto che </span><span class="hps">un insieme di funzioni</span> <span class="hps">o semplicemente </span><span class="hps">un elenco</span> <span class="hps">di istruzioni per il</span> <span class="hps">computer (come è nella visione tradizionale).</span> <span class="hps">In</span> <span class="hps">OOP</span><span>,</span> <span class="hps">ogni oggetto è</span> <span class="hps">in grado di ricevere</span> <span class="hps">messaggi</span><span>,</span> <span class="hps">elaborare dati</span><span>,</span> <span class="hps">e</span> <span class="hps">inviare messaggi</span> <span class="hps">ad altri oggetti</span><span>.</span> <span class="hps">Ogni oggetto</span> <span class="hps">può essere visto come</span> <span class="hps">una</span> <span class="hps">piccola macchina</span> <span class="hps">indipendente con</span> </span><span lang="it"><span class="hps">ruolo o</span> <span class="hps">responsabilità</span><span> distinti.</span></span></p>

<p><span id="result_box" lang="it"><span class="hps">OOP</span> <span class="hps">promuove una maggiore</span> <span class="hps">flessibilità e</span> mantenibilità <span class="hps">nella</span> <span class="hps">programmazione</span><span>,</span> <span class="hps">ed è</span> <span class="hps">molto popolare</span> <span class="hps">in</span> <span class="hps">ingegneria del software su larga scala</span><span>.</span> <span class="hps">Poiché</span> <span class="hps">OOP</span> <span class="hps">sottolinea con forza</span> <span class="hps">la modularità</span><span>,</span> <span class="hps">il codice</span> <span class="hps">object-oriented</span> <span class="hps">è più semplice da</span> <span class="hps">sviluppare e</span> <span class="hps">più facile da capire</span> <span class="hps">in seguito.</span> <span class="hps">Il codice</span> <span class="hps">object-oriented</span> <span class="hps">promuove</span> <span class="hps">un'analisi</span><span>,</span> <span class="hps">codifica</span><span>,</span> <span class="hps">e comprensione</span> <span class="hps">di</span> <span class="hps">situazioni</span></span><span lang="it"><span class="hps"> e</span> <span class="hps">procedure</span></span><span id="result_box" lang="it"><span class="hps"> complesse</span></span><span lang="it"><span class="hps"> più</span> <span class="hps">diretta</span> <span class="hps">che con</span> <span class="hps">metodi di programmazione</span> <span class="hps">a minor modularità</span></span><sup>.</sup><a href="https://developer.mozilla.org/it/docs/Web/JavaScript/Introduzione_al_carattere_Object-Oriented_di_JavaScript$edit#cite-1"><sup>1</sup></a></p>

<h2 id="Terminology" name="Terminology">Terminologia</h2>

<dl>
 <dt>{{Glossary("Namespace")}}</dt>
 <dd><span id="result_box" lang="it"><span class="hps">Un contenitore</span> <span class="hps">che</span> <span class="hps">consente agli sviluppatori di</span> <span class="hps">includere tutte</span> <span class="hps">le funzionalità</span> <span class="hps">sotto</span> <span class="hps">un</span> <span class="hps">nome unico, specifico per l'</span><span class="hps">applicazione</span><span>.</span></span></dd>
 <dt>{{Glossary("Class")}}</dt>
 <dd><span id="result_box" lang="it"><span class="hps">Definisce</span> <span class="hps">le caratteristiche dell'oggetto</span><span>.</span> <span class="hps">Una classe</span> <span class="hps">è una definizione</span> <span class="hps">del modello,</span> <span class="hps">delle proprietà e dei metodi</span> <span class="hps">di un oggetto</span><span>.</span></span></dd>
 <dt>{{Glossary("Object")}}</dt>
 <dd>Istanza di una classe.</dd>
 <dt>{{Glossary("Property")}}</dt>
 <dd>Una caratteristica di un oggetto, come un colore.</dd>
 <dt>{{Glossary("Method")}}</dt>
 <dd>Una capacità di un oggetto, come ad esempio cammina. È una procedura o funzione associata a una classe.</dd>
 <dt>{{Glossary("Constructor")}}</dt>
 <dd>Un metodo invocato nel momento in cui l'oggetto viene istanziato. Di solito ha lo stesso nome della classe che lo contiene.</dd>
 <dt>{{Glossary("Inheritance")}}</dt>
 <dd>Una classe può ereditare caratteristiche da un'altra classe.</dd>
 <dt>{{Glossary("Encapsulation")}}</dt>
 <dd>Una modalità di raggruppamento di dati e metodi che ne fanno uso.</dd>
 <dt>{{Glossary("Abstraction")}}</dt>
 <dd>L'insieme del complesso di eredità, metodi e proprietà di un oggetto deve rispecchiare adeguatamente un modello reale.</dd>
 <dt>{{Glossary("Polymorphism")}}</dt>
 <dd><span id="result_box" lang="it"><span class="hps">Poly </span><span class="hps">significa</span> <span class="hps">"<em>molti</em>"</span> <span class="hps">e</span> <span class="hps">morfismo</span> <span class="hps">significa</span> <span class="hps">"<em>forme</em>"</span><span>.</span> <span class="hps">Classi diverse </span><span class="hps">potrebbero</span> <span class="hps">definire lo stesso</span> <span class="hps">metodo o proprietà</span><span>.</span></span></dd>
</dl>



<p><span id="result_box" lang="it"><span class="hps">Per una</span> <span class="hps">descrizione</span> </span><span lang="it"><span class="hps">più ampia</span> <span class="hps">della programmazione</span> <span class="hps">orientata agli oggetti</span><span>, vedi</span> </span>{{interwiki("wikipedia", "Object-oriented programming")}}<span lang="it"> <span class="hps">su Wikipedia</span><span>.</span></span></p>



<h2 id="Programmazione_prototype-based">Programmazione  prototype-based</h2>

<p><span id="result_box" lang="it"><span class="hps">La programmazione p</span></span>rototype-based<span lang="it"><span class="hps"> (basata</span> <span class="hps">sul prototipo)</span> <span class="hps">è un modello</span> <span class="hps">OOP</span> <span class="hps">che non utilizza</span> <span class="hps">le classi</span><span>,</span> <span class="hps">ma piuttosto</span> <span class="hps">prima</span> <span class="hps">completa</span> <span class="hps">il comportamento di</span> <span class="hps">qualsiasi classe</span> <span class="hps">e</span> <span class="hps">poi</span> <span class="hps">riutilizza</span> <span class="atn hps">(</span><span>equivalente</span> <span class="hps">all'</span><span class="hps">ereditarietà</span> <span class="hps">nei linguaggi</span> <span class="hps">basati su classi</span><span>)</span> arricchendo <span class="atn hps">(</span><span>o sviluppando</span><span>)</span> <span class="hps">oggetti <em>prototipo</em></span><span class="hps"> esistenti</span><span>.</span> <span class="atn hps">(</span><span>Chiamata anche</span> <span class="hps">senza classi (</span></span>classless<span lang="it"><span class="hps">)</span><span>,</span> <span class="hps">orientata al prototipo</span><span> (</span></span>prototype-oriented<span lang="it"><span>),</span> <span class="hps">o</span> <span class="hps">programmazione basata</span> su <span class="hps">istanza</span><span> (</span></span>instance-based<span lang="it"><span>).</span><span>)</span></span></p>

<p><span id="result_box" lang="it"><span class="hps">L'esempio </span></span><span lang="it"><span class="hps">originale</span> <span class="atn hps">(</span><span>e più</span> <span class="hps">canonico</span><span>)</span> <span class="hps"> di un</span> <span class="hps">linguaggio basato sui prototipi</span> <span class="hps">è</span> </span>{{interwiki("wikipedia", "Self (programming language)", "Self")}}<span lang="it"> <span class="hps">sviluppato da</span> <span class="hps">David</span> <span class="hps">Ungar</span> <span class="hps">e Randall</span> <span class="hps">Smith</span><span>.</span> <span class="hps">Tuttavia lo</span> <span class="hps">stile di programmazione</span> <span class="atn hps">senza classi diventa</span> <span class="hps">sempre più popolare</span> <span class="hps">negli ultimi tempi,</span> <span class="hps">ed è stato adottato</span> <span class="hps">per</span> <span class="hps">i linguaggi di programmazione</span> <span class="hps">come JavaScript</span><span>,</span> <span class="hps">Cecil</span><span>,</span> <span class="hps">NewtonScript</span><span>,</span> <span class="hps">Io,</span> <span class="hps">MOO</span><span>,</span> <span class="hps">REBOL</span><span>,</span> <span class="hps">Kevo</span><span>,</span> <span class="hps">Squeak</span> <span class="atn hps">(</span><span>quando si utilizza il</span> <span class="hps">framework</span> </span>Viewer per<span lang="it"><span class="hps"> manipolare</span> <span class="hps">componenti</span> <span class="hps">Morphic</span><span>)</span><span>,</span> <span class="hps">e</span> <span class="hps">molti altri</span></span>.<a href="https://developer.mozilla.org/it/docs/Web/JavaScript/Introduzione_al_carattere_Object-Oriented_di_JavaScript$edit#cite-1"><sup>1</sup></a></p>

<h2 id="JavaScript_Object_Oriented_Programming" name="JavaScript_Object_Oriented_Programming">Programmazione  Object Oriented in JavaScript</h2>

<h3 id="Namespace">Namespace</h3>

<p>Un namespace <span id="result_box" lang="it"><span class="hps">è un contenitore</span> <span class="hps">che</span> <span class="hps">consente agli sviluppatori di</span> <span class="hps">includere tutte</span> <span class="hps">le funzionalità</span> <span class="hps">sotto</span> <span class="hps">un</span> <span class="hps">nome unico, specifico per l'</span><span class="hps">applicazione</span></span>. <strong>In JavaScript un namespace è solo un altro oggetto che contiene metodi, proprietà e oggetti.</strong></p>

<div class="note">
<p><strong>Nota:</strong> È <span lang="it"><span>importante notare che</span> <span class="hps">in JavaScript</span> <span class="hps">non c'è alcuna differenza</span> <span class="hps">a livello di</span> <span class="hps">linguaggio</span> <span class="hps">tra oggetti</span> <span class="hps">regolari e </span>namespace<span>.</span> <span class="hps">Questo</span> <span class="hps">differenzia da molti altri</span> <span class="hps">linguaggi orientati agli oggetti</span> <span class="hps">e può essere fonte</span><span class="hps"> di confusione</span> <span class="hps">per i nuovi</span> <span class="hps">programmatori JavaScript</span></span>.</p>
</div>

<p><span id="result_box" lang="it"><span class="hps">L'idea alla base</span> del<span class="hps">la creazione di</span> <span class="hps">un namespace</span> <span class="hps">in JavaScript</span> <span class="hps">è</span> <span class="hps">semplice: creare</span> <span class="hps">un oggetto</span> <span class="hps">globale</span><span>,</span> <span class="hps">e</span> <span class="hps">tutte le variabili</span><span>,</span> <span class="hps">i metodi</span> <span class="hps">e le funzioni</span> <span class="hps">diventano</span> <span class="hps">proprietà di tale oggetto</span><span>.</span> <span class="hps">L'uso</span> <span class="hps">dei namespace</span> <span class="hps">riduce anche</span> <span class="hps">il rischio di</span> <span class="hps">conflitti tra nomi</span> <span class="hps">in un'applicazione</span><span>,</span> <span class="hps">poiché gli oggetti</span> <span class="hps">di ciascuna applicazione</span> <span class="hps">sono</span> <span class="hps">proprietà di un</span> <span class="hps">oggetto globale</span> <span class="hps">definito dall'applicazione</span><span>.</span></span></p>

<p>Creiamo un oggetto globale chiamato MYAPP:</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="comment token">// global namespace</span>
<span class="keyword token">var</span> MYAPP <span class="operator token">=</span> MYAPP <span class="operator token">||</span> <span class="punctuation token">{</span><span class="punctuation token">}</span><span class="punctuation token">;</span></code></pre>

<p><span id="result_box" lang="it"><span class="hps">Nel</span> <span class="hps">codice di esempio di</span> <span class="hps">sopra</span> prima viene testato <span class="hps">se</span> <span class="hps">MYAPP</span> <span class="hps">è già definito</span> <span class="hps">(sia nello</span> <span class="hps">stesso o</span> <span class="hps">in un altro file</span><span>)</span><span>.</span> <span class="hps">Se sì, allora</span> <span class="atn hps">viene utilizzato l'</span><span class="hps">oggetto globale </span></span><span lang="it"><span>MYAPP già</span> <span class="hps">esistente</span><span>,</span> <span class="hps">altrimenti</span> viene creato<span class="hps"> un oggetto</span> <span class="hps">vuoto chiamato</span> <span class="hps">MYAPP</span> <span class="hps">che</span> <span class="hps">incapsula</span> <span class="hps">metodi,</span> <span class="hps">funzioni, variabili</span> <span class="hps">e oggetti</span><span>.</span></span></p>

<p>Possaimo anche creare sotto-namespace (tieni presente che l'oggetto globale deve essere definito prima):</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="comment token">// sub namespace</span>
MYAPP<span class="punctuation token">.</span>event <span class="operator token">=</span> <span class="punctuation token">{</span><span class="punctuation token">}</span><span class="punctuation token">;</span></code></pre>

<p><span id="result_box" lang="it"><span class="hps">La seguente</span> <span class="hps">è</span> <span class="hps">la sintassi del codice</span> <span class="hps">per</span> <span class="hps">la creazione di un</span> namespace <span class="hps">e l'aggiunta di</span> <span class="hps">variabili, funzioni</span><span>,</span> <span class="hps">e</span> <span class="hps">un metodo:</span></span></p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="comment token">// Create container called MYAPP.commonMethod for common method and properties</span>
MYAPP<span class="punctuation token">.</span>commonMethod <span class="operator token">=</span> <span class="punctuation token">{</span>
  regExForName<span class="punctuation token">:</span> <span class="string token">""</span><span class="punctuation token">,</span> <span class="comment token">// define regex for name validation</span>
  regExForPhone<span class="punctuation token">:</span> <span class="string token">""</span><span class="punctuation token">,</span> <span class="comment token">// define regex for phone no validation</span>
  validateName<span class="punctuation token">:</span> <span class="keyword token">function</span><span class="punctuation token">(</span>name<span class="punctuation token">)</span><span class="punctuation token">{</span>
    <span class="comment token">// Do something with name, you can access regExForName variable</span>
    <span class="comment token">// using "this.regExForName"</span>
  <span class="punctuation token">}</span><span class="punctuation token">,</span>

  validatePhoneNo<span class="punctuation token">:</span> <span class="keyword token">function</span><span class="punctuation token">(</span>phoneNo<span class="punctuation token">)</span><span class="punctuation token">{</span>
    <span class="comment token">// do something with phone number</span>
  <span class="punctuation token">}</span>
<span class="punctuation token">}</span>

<span class="comment token">// Object together with the method declarations</span>
MYAPP<span class="punctuation token">.</span>event <span class="operator token">=</span> <span class="punctuation token">{</span>
    addListener<span class="punctuation token">:</span> <span class="keyword token">function</span><span class="punctuation token">(</span>el<span class="punctuation token">,</span> type<span class="punctuation token">,</span> fn<span class="punctuation token">)</span> <span class="punctuation token">{</span>
    <span class="comment token">// code stuff</span>
    <span class="punctuation token">}</span><span class="punctuation token">,</span>
    removeListener<span class="punctuation token">:</span> <span class="keyword token">function</span><span class="punctuation token">(</span>el<span class="punctuation token">,</span> type<span class="punctuation token">,</span> fn<span class="punctuation token">)</span> <span class="punctuation token">{</span>
    <span class="comment token">// code stuff</span>
    <span class="punctuation token">}</span><span class="punctuation token">,</span>
    getEvent<span class="punctuation token">:</span> <span class="keyword token">function</span><span class="punctuation token">(</span>e<span class="punctuation token">)</span> <span class="punctuation token">{</span>
    <span class="comment token">// code stuff</span>
    <span class="punctuation token">}</span>

    <span class="comment token">// Can add another method and properties</span>
<span class="punctuation token">}</span>

<span class="comment token">// Syntax for Using addListener method:</span>
MYAPP<span class="punctuation token">.</span>event<span class="punctuation token">.</span><span class="function token">addListener</span><span class="punctuation token">(</span><span class="string token">"yourel"</span><span class="punctuation token">,</span> <span class="string token">"type"</span><span class="punctuation token">,</span> callback<span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<h3 id="Oggetti_incorporati_built-in_standard">Oggetti incorporati (built-in) standard</h3>

<p><span id="result_box" lang="it"><span class="hps">JavaScript</span> <span class="hps">ha diversi</span> <span class="hps">oggetti inclusi</span> <span class="hps">nel suo nucleo</span><span>,</span> <span class="hps">per esempio ci</span> <span class="hps">sono</span> <span class="hps">oggetti come</span> </span>Math, Object, Array e String<span lang="it"><span>.</span> <span class="hps">L'esempio seguente mostra</span> <span class="hps">come utilizzare</span> <span class="hps">l'oggetto</span> <span class="hps">Math per</span> <span class="hps">ottenere</span> <span class="hps">un numero casuale</span> <span class="hps">utilizzando</span> <span class="hps">il suo</span> <span class="hps">metodo</span></span> <code>random()</code> <span lang="it"><span>.</span></span></p>

<pre class="brush: js line-numbers  language-js"><code class="language-js">console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span>Math<span class="punctuation token">.</span><span class="function token">random</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<div class="note"><strong>Nota:</strong> <span id="result_box" lang="it"><span class="hps">Questo</span> <span class="hps">e</span> <span class="hps">tutti gli</span> <span class="hps">ulteriori esempi</span> presuppongono che <span class="hps">una funzione chiamata</span></span> {{domxref("console.log()")}} <span lang="it"><span class="hps">sia definita</span> <span class="hps">a livello globale</span><span>.</span> <span class="hps">La funzione</span> </span><code>console.log()</code> <span lang="it"><span class="hps">in realtà non</span> <span class="hps">è </span><span class="hps">parte</span> <span class="hps">di</span> <span class="hps">JavaScript</span> <span class="hps">in sé</span><span>,</span> <span class="hps">ma</span> <span class="hps">molti browser</span> la implementano <span class="hps">per aiutare</span> <span class="hps">il debug</span><span>.</span></span></div>

<p>Vedi <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects" title="en-US/docs/Web/JavaScript/Reference/Global_Objects">JavaScript Reference: Standard built-in objects</a> for una lista degli oggetti di nucleo in JavaScript.</p>

<p>Ogni oggetto in JavaScript è una instanza dell'oggetto <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object"><code>Object</code></a> e perciò ne eredita tutte le sue  proprietà e metodi.</p>

<h3 id="Oggetti_utente">Oggetti utente</h3>

<h4 id="La_classe">La classe</h4>

<p><span id="result_box" lang="it"><span class="hps">JavaScript è un linguaggio</span> <span class="hps">basato sui prototipi</span> <span class="hps">e</span> <span class="hps">non contiene</span> <span class="hps">alcuna dichiarazione</span> <span class="hps">di classe</span><span>,</span> <span class="hps">come invece si trova</span> <span class="hps">in C</span> <span class="hps">++</span> <span class="hps">o Java</span><span>.</span> <span class="hps">Questo a volte è</span> <span class="hps">fonte di confusione per</span> <span class="hps">i programmatori</span> <span class="hps">abituati</span> <span class="hps">ai linguaggi</span> <span class="hps">con</span> <span class="hps">una dichiarazione</span></span> <code>class</code><span lang="it"><span>.</span> <span class="hps">JavaScript</span> <span class="hps">utilizza le funzioni</span> <span class="hps">come</span> <span class="hps">costruttori</span> <span class="hps">per le classi</span><span>.</span> <span class="hps">Definire una</span> <span class="hps">classe è</span> <span class="hps">facile come</span> <span class="hps">definire una funzione</span><span>.</span> <span class="hps">Nell'esempio sottostante</span> <span class="hps">si definisce una</span> <span class="hps">nuova</span> <span class="hps">classe chiamata</span> <span class="hps">Person con</span> <span class="hps">un</span> <span class="hps">costruttore vuoto</span><span>.</span></span></p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span> <span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="punctuation token">{</span><span class="punctuation token">}</span><span class="punctuation token">;</span></code></pre>

<h4 id="Loggetto_istanza_di_classe">L'oggetto (istanza di classe)</h4>

<p>Per creare una nuova istanza di un oggetto <code>obj</code> utilizziamo l'istruzione <code>new obj</code> assegnando il risultato (che è di tipo <code>obj</code>) ad una variabile, per poi accedervi successivamente.</p>

<p>Nell'esempio precedente abbiamo definito una classe chiamata  <code>Person</code>. In quello seguente creiamo due istanze (<code>person1</code> e <code>person2</code>).</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> person1 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">var</span> person2 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<div class="note"><strong>Nota:</strong> Prego vedi {{jsxref("Object.create()")}} per un ulteriore nuovo metodo d'istanza che crea una istanza non inizializzata.</div>

<h4 id="Il_costruttore">Il costruttore</h4>

<p><span id="result_box" lang="it"><span class="hps">Il</span> <span class="hps">costruttore viene chiamato</span> quando si instanzia un oggetto <span class="atn hps">(</span><span>il momento in cui</span> <span class="hps">si crea</span> <span class="hps">l'istanza dell'oggetto</span><span>)</span><span>.</span> <span class="hps">Il</span> <span class="hps">costruttore è un</span> <span class="hps">metodo della classe</span><span>.</span> <span class="hps">In JavaScript</span> <span class="hps">la funzione</span> <span class="hps">funge da</span> <span class="hps">costruttore dell'oggetto</span><span>,</span> <span class="hps">pertanto</span> <span class="hps">non è necessario</span> <span class="hps">definire esplicitamente</span> <span class="hps">un</span> <span class="hps">metodo costruttore</span><span>.</span> <span class="hps">Ogni azione</span> <span class="hps">dichiarata</span> <span class="hps">nella classe</span> <span class="hps">viene eseguita</span> <span class="hps">al momento della</span> <span class="hps">creazione di un'istanza</span><span>.</span></span></p>

<p><span id="result_box" lang="it"><span class="hps">Il costruttore</span> <span class="hps">viene utilizzato per</span> <span class="hps">impostare le proprietà</span> <span class="hps">dell'oggetto</span> <span class="hps">o</span> <span class="hps">per chiamare</span> <span class="hps">i metodi che</span> <span class="atn hps">preparano l'</span><span>oggetto per il suo uso</span><span>.</span> <span class="hps">L'aggiunta di</span> <span class="hps">metodi di classe</span> <span class="hps">e le loro definizioni</span> <span class="hps">si effettua </span><span class="hps">utilizzando una</span> <span class="hps">sintassi diversa</span> <span class="hps">descritta più avanti in</span> <span class="hps">questo</span> <span class="hps">articolo</span><span>.</span></span></p>

<p>Nell'esempio seguente il costruttore della classe<code> Person</code> registra un messaggio quando viene istanziato un oggetto <code>Person</code>.</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span> <span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">'instance created'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="keyword token">var</span> person1 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">var</span> person2 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<h4 id="La_proprietà_attributo_di_oggetto">La proprietà (attributo di oggetto)</h4>

<p>Le proprietà sono variabili contenute nella classe; ogni istanza dell'oggetto ha queste proprietà. Le proprietà sono impostate nel costruttore (funzione) della classe in modo che siano creati su ogni istanza.</p>

<p><span id="result_box" lang="it"><span class="hps">La</span> <span class="hps">parola chiave</span></span> <code>this</code>, <span lang="it"><span class="hps">che si riferisce</span> <span class="hps">all'oggetto</span> <span class="hps">corrente</span><span>,</span> <span class="hps">consente di lavorare</span> <span class="hps">con le proprietà</span> <span class="hps">all'interno della classe</span><span>.</span> <span class="hps">L'accesso</span> <span class="atn hps">(</span><span>in lettura o</span> <span class="hps">scrittura)</span> <span class="hps">ad una proprietà</span> <span class="hps">al di fuori</span> <span class="hps">della classe</span> <span class="hps">è fatto con</span> <span class="hps">la sintassi</span><span>:</span> </span><code>NomeIstanza.Proprietà</code><span lang="it"><span>,</span> <span class="hps">proprio come in</span> <span class="hps">C</span> <span class="hps">++</span><span>,</span> <span class="hps">Java</span><span>,</span> <span class="hps">e molti altri linguaggi</span><span>.</span> <span class="atn hps">(</span><span>All'interno della</span> <span class="hps">classe la</span> <span class="hps">sintassi </span></span><code>this.Proprietà</code><span lang="it"><span class="hps"> è utilizzata</span> <span class="hps">per ottenere o impostare</span> <span class="hps">il valore della proprietà</span><span>.</span><span>)</span></span></p>

<p>Nell'esempio seguente, definiamo al momento della creazione  la proprietà <code>firstName</code> per la classe <code>Person</code>:</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span> <span class="punctuation token">(</span>firstName<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  <span class="keyword token">this</span><span class="punctuation token">.</span>firstName <span class="operator token">=</span> firstName<span class="punctuation token">;</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">'Person instantiated'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="keyword token">var</span> person1 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="string token">'Alice'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">var</span> person2 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="string token">'Bob'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// Show the firstName properties of the objects</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">'person1 is '</span> <span class="operator token">+</span> person1<span class="punctuation token">.</span>firstName<span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// logs "person1 is Alice"</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">'person2 is '</span> <span class="operator token">+</span> person2<span class="punctuation token">.</span>firstName<span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// logs "person2 is Bob"</span></code></pre>

<h4 id="I_metodi">I metodi</h4>

<p>I metodi sono funzioni (e definiti come funzioni), ma per il resto seguono la stessa logica delle proprietà. Chiamare un metodo è simile all'accesso a una proprietà, ma si aggiunge () alla fine del nome del metodo, eventualmente con argomenti. Per definire un metodo va assegnata una funzione a una proprietà della proprietà <code>prototype</code> della classe. In seguito sarà possibile chiamare il metodo sull'oggetto utilizzando lo stesso nome assegnato alla funzione.</p>

<p>Nell'esempio seguente definiamo e usiamo il metodo <code>sayHello()</code> per la classe <code>Person</code>.</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span> <span class="punctuation token">(</span>firstName<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  <span class="keyword token">this</span><span class="punctuation token">.</span>firstName <span class="operator token">=</span> firstName<span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

Person<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>sayHello <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">"Hello, I'm "</span> <span class="operator token">+</span> <span class="keyword token">this</span><span class="punctuation token">.</span>firstName<span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="keyword token">var</span> person1 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="string token">"Alice"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">var</span> person2 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="string token">"Bob"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// call the Person sayHello method.</span>
person1<span class="punctuation token">.</span><span class="function token">sayHello</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// logs "Hello, I'm Alice"</span>
person2<span class="punctuation token">.</span><span class="function token">sayHello</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// logs "Hello, I'm Bob"</span></code></pre>

<p>In JavaScript i metodi sono oggetti funzione regolarmente associati a un oggetto come una proprietà, il che significa che è possibile richiamare i metodi "fuori dal contesto". Si consideri il seguente codice di esempio:</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span> <span class="punctuation token">(</span>firstName<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  <span class="keyword token">this</span><span class="punctuation token">.</span>firstName <span class="operator token">=</span> firstName<span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

Person<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>sayHello <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">"Hello, I'm "</span> <span class="operator token">+</span> <span class="keyword token">this</span><span class="punctuation token">.</span>firstName<span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="keyword token">var</span> person1 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="string token">"Alice"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">var</span> person2 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span><span class="string token">"Bob"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="keyword token">var</span> helloFunction <span class="operator token">=</span> person1<span class="punctuation token">.</span>sayHello<span class="punctuation token">;</span>

<span class="comment token">// logs "Hello, I'm Alice"</span>
person1<span class="punctuation token">.</span><span class="function token">sayHello</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// logs "Hello, I'm Bob"</span>
person2<span class="punctuation token">.</span><span class="function token">sayHello</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// logs "Hello, I'm undefined" (or fails</span>
<span class="comment token">// with a TypeError in strict mode)</span>
<span class="function token">helloFunction</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// logs true</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span>helloFunction <span class="operator token">===</span> person1<span class="punctuation token">.</span>sayHello<span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// logs true</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span>helloFunction <span class="operator token">===</span> Person<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>sayHello<span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// logs "Hello, I'm Alice"</span>
helloFunction<span class="punctuation token">.</span><span class="function token">call</span><span class="punctuation token">(</span>person1<span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<p>Come dimostra questo esempio tutti i riferimenti alla funzione <code>sayHello</code> — quello su  <code>person1</code>, su <code>Person.prototype</code>, nella variabile <code>helloFunction</code>, ecc.— si riferiscono tutti alla <em>stessa funzione</em>. Il valore di <code>this</code> nel corso di una chiamata alla funzione dipende da come noi lo chiamiamo. Più comunemente, quando chiamiamo <code>this</code>  in un'espressione dove abbiamo ottenuto la funzione da una proprietà di oggetto — <code>person1.sayHello()</code>— <code>this</code> è riferito all'oggetto da cui abbiamo ottenuto la funzione (<code>person1</code>), questa è la ragione per cui <code>person1.sayHello()</code> usa il  nome "Alice" e <code>person2.sayHello()</code> usa il nome "Bob".  Ma se lo chiamiamo in altri modi, <code>this</code> è impostato in modo diverso: chiamare <code>this</code> da una variabile— <code>helloFunction()</code>— <code>imposta this</code> come riferimento all'oggetto globale (<code>window</code>, sui browser). Dal momento che l'oggetto globale (probabilmente) non dispone di una proprietà <code>firstName</code> otteniamo "Hello, I'm undefined". (Questo accade in modalità blanda (loose mode); sarebbe stato diverso [un errore] in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode" title="/en/docs/Web/JavaScript/Reference/Functions_and_function_scope/Strict_mode">strict mode</a>, ma per evitare confusione qui non entreremo nei dettagli). Oppure si può impostare  <code>this</code> esplicitamente utilizzando <code>Function#call</code> (o <code>Function#apply</code>), come illustrato alla fine dell'esempio.</p>

<div class="note"><strong>Nota:</strong> Vedi approfondimenti su <code>this</code> in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call" title="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/call">Function#call</a> e <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/apply" title="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/apply">Function#apply</a></div>

<h4 id="Eredità">Eredità</h4>

<p>L'ereditarietà è un modo per creare una classe come una versione specializzata di una o più classi (<em>JavaScript supporta solo l'ereditarietà singola</em>). La classe specializzata viene comunemente chiamata <em>figlio</em>, e l'altra classe viene comunemente chiamato <em>padre</em>. In JavaScript si esegue questa operazione assegnando un'istanza della classe padre alla classe figlio, e poi specializzandola. Nel browser moderni è anche possibile utilizzare <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create#Classical_inheritance_with_Object.create" title="/en-US/docs/JavaScript/Reference/Global_Objects/Object/create#Classical_inheritance_with_Object.create">Object.create</a> per implementare l'ereditarietà.</p>

<div class="note">
<p><strong>Nota:</strong> JavaScript non rileva  <code>prototype.constructor</code> della classe figlio (vedi <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype">Object.prototype</a>), quindi devi farlo manualmente. Vedi la domanda "<a href="http://stackoverflow.com/questions/8453887/why-is-it-necessary-to-set-the-prototype-constructor">Why is it necessary to set the prototype constructor?</a>" su Stackoverflow.</p>
</div>

<p>Nell'esempio seguente definiamo la classe  <code>Student</code> come classe figlio di <code>Person</code>. Quindi ridefiniamo il metodo <code>sayHello()</code> e aggiungiamo il metodo <code>sayGoodBye()</code> .</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="comment token">// Define the Person constructor</span>
<span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span>firstName<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  <span class="keyword token">this</span><span class="punctuation token">.</span>firstName <span class="operator token">=</span> firstName<span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="comment token">// Add a couple of methods to Person.prototype</span>
Person<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>walk <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">"I am walking!"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

Person<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>sayHello <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">"Hello, I'm "</span> <span class="operator token">+</span> <span class="keyword token">this</span><span class="punctuation token">.</span>firstName<span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="comment token">// Define the Student constructor</span>
<span class="keyword token">function</span> <span class="function token">Student</span><span class="punctuation token">(</span>firstName<span class="punctuation token">,</span> subject<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  <span class="comment token">// Call the parent constructor, making sure (using Function#call)</span>
  <span class="comment token">// that "this" is set correctly during the call</span>
  Person<span class="punctuation token">.</span><span class="function token">call</span><span class="punctuation token">(</span><span class="keyword token">this</span><span class="punctuation token">,</span> firstName<span class="punctuation token">)</span><span class="punctuation token">;</span>

  <span class="comment token">// Initialize our Student-specific properties</span>
  <span class="keyword token">this</span><span class="punctuation token">.</span>subject <span class="operator token">=</span> subject<span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="comment token">// Create a Student.prototype object that inherits from Person.prototype.</span>
<span class="comment token">// Note: A common error here is to use "new Person()" to create the</span>
<span class="comment token">// Student.prototype. That's incorrect for several reasons, not least </span>
<span class="comment token">// that we don't have anything to give Person for the "firstName" </span>
<span class="comment token">// argument. The correct place to call Person is above, where we call </span>
<span class="comment token">// it from Student.</span>
Student<span class="punctuation token">.</span>prototype <span class="operator token">=</span> Object<span class="punctuation token">.</span><span class="function token">create</span><span class="punctuation token">(</span>Person<span class="punctuation token">.</span>prototype<span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// See note below</span>

<span class="comment token">// Set the "constructor" property to refer to Student</span>
Student<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>constructor <span class="operator token">=</span> Student<span class="punctuation token">;</span>

<span class="comment token">// Replace the "sayHello" method</span>
Student<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>sayHello <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">"Hello, I'm "</span> <span class="operator token">+</span> <span class="keyword token">this</span><span class="punctuation token">.</span>firstName <span class="operator token">+</span> <span class="string token">". I'm studying "</span>
              <span class="operator token">+</span> <span class="keyword token">this</span><span class="punctuation token">.</span>subject <span class="operator token">+</span> <span class="string token">"."</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="comment token">// Add a "sayGoodBye" method</span>
Student<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>sayGoodBye <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">{</span>
  console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">"Goodbye!"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="comment token">// Example usage:</span>
<span class="keyword token">var</span> student1 <span class="operator token">=</span> <span class="keyword token">new</span> <span class="class-name token">Student</span><span class="punctuation token">(</span><span class="string token">"Janet"</span><span class="punctuation token">,</span> <span class="string token">"Applied Physics"</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
student1<span class="punctuation token">.</span><span class="function token">sayHello</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>   <span class="comment token">// "Hello, I'm Janet. I'm studying Applied Physics."</span>
student1<span class="punctuation token">.</span><span class="function token">walk</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>       <span class="comment token">// "I am walking!"</span>
student1<span class="punctuation token">.</span><span class="function token">sayGoodBye</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// "Goodbye!"</span>

<span class="comment token">// Check that instanceof works correctly</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span>student1 <span class="keyword token">instanceof</span> <span class="class-name token">Person</span><span class="punctuation token">)</span><span class="punctuation token">;</span>  <span class="comment token">// true </span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span>student1 <span class="keyword token">instanceof</span> <span class="class-name token">Student</span><span class="punctuation token">)</span><span class="punctuation token">;</span> <span class="comment token">// true</span></code></pre>

<p>Per quanto riguarda la linea <code>Student.prototype = Object.create(Person.prototype);</code> : in vecchi interpreti JavaScript senza  <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create" title="Object.create"><code>Object.create</code></a>, si può utilizzare un "polyfill" (anche detto "shim", vedi l'articolo collegato), oppure utilizzare una funzione che produce il medesimo risultato, come:</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">function</span> <span class="function token">createObject</span><span class="punctuation token">(</span>proto<span class="punctuation token">)</span> <span class="punctuation token">{</span>
    <span class="keyword token">function</span> <span class="function token">ctor</span><span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="punctuation token">{</span> <span class="punctuation token">}</span>
    ctor<span class="punctuation token">.</span>prototype <span class="operator token">=</span> proto<span class="punctuation token">;</span>
    <span class="keyword token">return</span> <span class="keyword token">new</span> <span class="class-name token">ctor</span><span class="punctuation token">(</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span>

<span class="comment token">// Usage:</span>
Student<span class="punctuation token">.</span>prototype <span class="operator token">=</span> <span class="function token">createObject</span><span class="punctuation token">(</span>Person<span class="punctuation token">.</span>prototype<span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<div class="note"><strong>Nota:</strong> Vedi <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create" title="Object.create">Object.create</a> per maggiori informazioni su ciò che fa uno shim per vecchi interpreti.</div>

<p>Essere sicuri che  <code>this</code> punti alla cosa giusta a prescindere da come l'oggetto sia istanziato può essere difficile. Tuttavia c'e una tecnica semplice per renderlo più facile.</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> Person <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span>firstName<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  <span class="keyword token">if</span> <span class="punctuation token">(</span><span class="keyword token">this</span> <span class="keyword token">instanceof</span> <span class="class-name token">Person</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
    <span class="keyword token">this</span><span class="punctuation token">.</span>firstName <span class="operator token">=</span> firstName<span class="punctuation token">;</span>
  <span class="punctuation token">}</span> <span class="keyword token">else</span> <span class="punctuation token">{</span>
    <span class="keyword token">return</span> <span class="keyword token">new</span> <span class="class-name token">Person</span><span class="punctuation token">(</span>firstName<span class="punctuation token">)</span><span class="punctuation token">;</span>
  <span class="punctuation token">}</span>
<span class="punctuation token">}</span></code></pre>

<h4 id="Incapsulamento">Incapsulamento</h4>

<p>Nell'esempio precedente <code>Student</code> non ha bisogno di sapere come sia realizzato il metodo <code>walk()</code> della classe <code>Person</code>, ma può comunque utilizzarlo; la classe <code>Student</code> non ha bisogno di definire in modo esplicito questo metodo se non vogliamo cambiarlo. Questo è chiamato <strong>incapsulamento</strong>, per cui ogni classe impacchetta dati e metodi in una singola unità.</p>

<p>Il nascondere informazioni (information hiding) è una caratteristica comune ad altre linguaggi, spesso in forma di  metodi / proprietà private e protette. Anche se si potrebbe simulare qualcosa di simile in JavaScript, questo non è un requisito per fare programmazione Object Oriented.<a href="https://developer.mozilla.org/it/docs/Web/JavaScript/Introduzione_al_carattere_Object-Oriented_di_JavaScript$edit#cite-2"><sup>2</sup></a></p>

<h4 id="Astrazione">Astrazione</h4>

<p>L'astrazione è un meccanismo che permette di modellare la parte corrente del problema, sia con eredità (specializzazione) o la composizione. JavaScript ottiene la specializzazione per eredità, e la composizione permettendo che istanze di classe siano valori di attributi di altri oggetti.</p>

<p>La classe Function di Javascript eredita dalla classe Object (questo dimostra la specializzazione del modello) e la proprietà Function.prototype è un'istanza di oggetto (ciò dimostra la composizione).</p>

<p>The JavaScript Function class inherits from the Object class (this demonstrates specialization of the model) and the Function.prototype property is an instance of Object (this demonstrates composition).</p>

<pre class="brush: js line-numbers  language-js"><code class="language-js"><span class="keyword token">var</span> foo <span class="operator token">=</span> <span class="keyword token">function</span> <span class="punctuation token">(</span><span class="punctuation token">)</span> <span class="punctuation token">{</span><span class="punctuation token">}</span><span class="punctuation token">;</span>

<span class="comment token">// logs "foo is a Function: true"</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">'foo is a Function: '</span> <span class="operator token">+</span> <span class="punctuation token">(</span>foo <span class="keyword token">instanceof</span> <span class="class-name token">Function</span><span class="punctuation token">)</span><span class="punctuation token">)</span><span class="punctuation token">;</span>

<span class="comment token">// logs "foo.prototype is an Object: true"</span>
console<span class="punctuation token">.</span><span class="function token">log</span><span class="punctuation token">(</span><span class="string token">'foo.prototype is an Object: '</span> <span class="operator token">+</span> <span class="punctuation token">(</span>foo<span class="punctuation token">.</span>prototype <span class="keyword token">instanceof</span> <span class="class-name token">Object</span><span class="punctuation token">)</span><span class="punctuation token">)</span><span class="punctuation token">;</span></code></pre>

<h4 id="Polimorfismo">Polimorfismo</h4>

<p>Così come tutti i metodi e le proprietà sono definite all'interno della proprietà prototype, classi diverse possono definire metodi con lo stesso nome; i metodi sono nell'ambito della classe in cui sono definiti, a meno che le due classi siano in un rapporto padre-figlio (cioè una eredita dall'altra in una catena di ereditarietà).</p>



<h2 id="Notes" name="Notes">Note</h2>

<p>Le tecniche presentate in questo articolo per attuare la programmazione orientata agli oggetti non sono le uniche che possono essere utilizzate in JavaScript, che è molto flessibile in termini di come la programmazione orientata agli oggetti possa essere eseguita.</p>

<p>Allo stesso modo, le tecniche qui indicate non usano alcuna violazione di linguaggio, né imitano implementazioni di teorie di oggetti di altri linguaggi.</p>

<p>Ci sono altre tecniche che rendono la programmazione orientata agli oggetti in JavaScript ancora più avanzata, ma sono oltre la portata di questo articolo introduttivo.</p>

<h2 id="References" name="References">Riferimenti</h2>

<ol>
 <li>{{ Ref() }} Mozilla. "Core JavaScript 1.5 Guide", http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide</li>
 <li>{{ Ref() }} wikipedia. "Object-oriented programming", <a class="external" href="http://en.wikipedia.org/wiki/Object-oriented_programming" rel="freelink">http://en.wikipedia.org/wiki/Object-...ed_programming</a></li>
</ol>

<div class="originaldocinfo">
<p><strong>Original Document Information</strong></p>

<ul>
 <li>Author(s): Fernando Trasviña &lt;f_trasvina at hotmail dot com&gt;</li>
 <li>Copyright Information: © 1998-2005 by individual mozilla.org contributors; content available under a <a class="external" href="http://www.mozilla.org/foundation/licensing/website-content.html">Creative Commons license</a></li>
</ul>
</div>

<p>{{ languages( { "es": "es/Introducción_a_JavaScript_orientado_a_objetos"} ) }}</p>