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+---
+title: instanceof
+slug: Web/JavaScript/Reference/Operators/instanceof
+translation_of: Web/JavaScript/Reference/Operators/instanceof
+---
+<div>{{jsSidebar("Operators")}}</div>
+
+<div>O operador <strong><code>instanceof</code></strong> testa se um objeto tem, em seu prototype, a função construtora.</div>
+
+<h2 id="Sintaxe">Sintaxe</h2>
+
+<pre class="syntaxbox"><em>objeto</em> instanceof <em>construtor</em></pre>
+
+<h3 id="Parâmetros">Parâmetros</h3>
+
+<dl>
+ <dt><code>objeto</code></dt>
+ <dd>O objeto a ser testado</dd>
+</dl>
+
+<dl>
+ <dt><code>construtor</code></dt>
+ <dd>Função construtora a ser verificada</dd>
+</dl>
+
+<h2 id="Descrição">Descrição</h2>
+
+<p>O operador <span style="font-family: Consolas, Monaco, 'Andale Mono', monospace;">instanceof</span> testa a presença da função construtora no prototype do objeto.</p>
+
+<pre class="brush: js">// defenindo construtores
+function C(){}
+function D(){}
+
+var o = new C();
+
+// true, porque: Object.getPrototypeOf(o) === C.prototype
+o instanceof C;
+
+// false, porque D.prototype não está no prototype desse objeto
+o instanceof D;
+
+o instanceof Object; // true, porque:
+C.prototype instanceof Object // true
+
+C.prototype = {};
+var o2 = new C();
+
+o2 instanceof C; // true
+
+// false, porque C.prototype não está mais no prototype desse objeto
+o instanceof C;
+
+D.prototype = new C(); // use inheritance
+var o3 = new D();
+o3 instanceof D; // true
+o3 instanceof C; // true
+</pre>
+
+<p>Note que o resultado do <span style="font-family: Consolas, Monaco, 'Andale Mono', monospace;">instanceof</span> pode alterar quando a gente altera o prototype da função construtora. No entanto, a gente não pode alterar (por padrão) o prototype do objeto. Só é possível fazer essa alteração usando a pseudopropriedade <span style="font-family: Consolas, Monaco, 'Andale Mono', monospace;">__proto__.</span></p>
+
+<h3 id="instanceof_and_multiple_context_(e.g._frames_or_windows)"><code>instanceof</code> and multiple context (e.g. frames or windows)</h3>
+
+<p>Different scope have different execution environments. This means that they have different built-ins (different global object, different constructors, etc.). This may result in unexpected results. For instance, <code>[] instanceof window.frames[0].Array</code> will return <code>false</code>, because <code>Array.prototype !== </code><code>window.frames[0].Array</code> and arrays inherit from the former. This may not make sense at first but when you start dealing with multiple frames or windows in your script and pass objects from one context to another via functions, this will be a valid and strong issue. For instance, you can securely check if a given object is in fact an Array using <code>Array.isArray(myObj)</code></p>
+
+<div class="note"><strong>Note for Mozilla developers:</strong><br>
+In code using XPCOM <code>instanceof</code> has special effect: <code>obj instanceof </code><em><code>xpcomInterface</code></em> (e.g. <code>Components.interfaces.nsIFile</code>) calls <code>obj.QueryInterface(<em>xpcomInterface</em>)</code> and returns <code>true</code> if QueryInterface succeeded. A side effect of such call is that you can use <em><code>xpcomInterface</code></em>'s properties on <code>obj</code> after a successful <code>instanceof</code> test. Unlike standard JavaScript globals, the test <code>obj instanceof xpcomInterface </code>works as expected even if <code>obj</code> is from a different scope.</div>
+
+<h2 id="Examples">Examples</h2>
+
+<h3 id="Demonstrating_that_String_and_Date_are_of_type_Object_and_exceptional_cases">Demonstrating that <code>String</code> and <code>Date</code> are of type <code>Object</code> and exceptional cases</h3>
+
+<p>The following code uses <code>instanceof</code> to demonstrate that <code>String</code> and <code>Date</code> objects are also of type <code>Object</code> (they are derived from <code>Object</code>).</p>
+
+<p>However, objects created with the object literal notation are an exception here: Although the prototype is undefined, <code>instanceof Object</code> returns <code>true</code>.</p>
+
+<pre class="brush: js">var simpleStr = "This is a simple string";
+var myString  = new String();
+var newStr    = new String("String created with constructor");
+var myDate    = new Date();
+var myObj     = {};
+
+simpleStr instanceof String; // returns false, checks the prototype chain, finds undefined
+myString  instanceof String; // returns true
+newStr    instanceof String; // returns true
+myString  instanceof Object; // returns true
+
+myObj instanceof Object;    // returns true, despite an undefined prototype
+({})  instanceof Object;    // returns true, same case as above
+
+myString instanceof Date;   // returns false
+
+myDate instanceof Date;     // returns true
+myDate instanceof Object;   // returns true
+myDate instanceof String;   // returns false
+</pre>
+
+<h3 id="Demonstrating_that_mycar_is_of_type_Car_and_type_Object">Demonstrating that <code>mycar</code> is of type <code>Car</code> and type <code>Object</code></h3>
+
+<p>The following code creates an object type <code>Car</code> and an instance of that object type, <code>mycar</code>. The <code>instanceof</code> operator demonstrates that the <code>mycar</code> object is of type <code>Car</code> and of type <code>Object</code>.</p>
+
+<pre class="brush: js">function Car(make, model, year) {
+  this.make = make;
+  this.model = model;
+  this.year = year;
+}
+var mycar = new Car("Honda", "Accord", 1998);
+var a = mycar instanceof Car;    // retorna true
+var b = mycar instanceof Object; // retorna true
+</pre>
+
+<h2 id="Especificações">Especificações</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">Especificação</th>
+   <th scope="col">Status</th>
+   <th scope="col">Comentário</th>
+  </tr>
+  <tr>
+   <td>ECMAScript 1st Edition.</td>
+   <td>Standard</td>
+   <td>Definição inicial. Implementada no JavaScript 1.4</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES5.1', '#sec-11.8.6', 'The instanceof operator')}}</td>
+   <td>{{Spec2('ES5.1')}}</td>
+   <td> </td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES6', '#sec-relational-operators', 'Relational Operators')}}</td>
+   <td>{{Spec2('ES6')}}</td>
+   <td> </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Compatibilidade_nos_navegadores">Compatibilidade nos navegadores</h2>
+
+<p>{{CompatibilityTable}}</p>
+
+<div id="compat-desktop">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Chrome</th>
+   <th>Firefox (Gecko)</th>
+   <th>Internet Explorer</th>
+   <th>Opera</th>
+   <th>Safari</th>
+  </tr>
+  <tr>
+   <td>Basic support</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<div id="compat-mobile">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Android</th>
+   <th>Chrome for Android</th>
+   <th>Firefox Mobile (Gecko)</th>
+   <th>IE Mobile</th>
+   <th>Opera Mobile</th>
+   <th>Safari Mobile</th>
+  </tr>
+  <tr>
+   <td>Basic support</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+   <td>{{CompatVersionUnknown}}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<h2 id="Veja_também">Veja também</h2>
+
+<ul>
+ <li><code><a href="/en-US/docs/Web/JavaScript/Reference/Operators/typeof" title="/en-US/docs/JavaScript/Reference/Operators/typeof">typeof</a></code></li>
+</ul>