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---
title: Object.prototype
slug: Web/JavaScript/Reference/Global_Objects/Object/prototype
tags:
- JavaScript
- Object
- Objeto
- Propriedade
translation_of: Web/JavaScript/Reference/Global_Objects/Object
translation_of_original: Web/JavaScript/Reference/Global_Objects/Object/prototype
---
<div>{{JSRef}}</div>
<p>A propriedade <code><strong>Object.prototype</strong></code> representa o <em>prototype object</em> {{jsxref("Object","Objeto")}} .</p>
<div>{{js_property_attributes(0, 0, 0)}}</div>
<h2 id="Descrição">Descrição</h2>
<p>Nearly all objects in JavaScript are instances of {{jsxref("Object")}}; a typical object inherits properties (including methods) from <code>Object.prototype</code>, although these properties may be shadowed (a.k.a. overridden). However, an <code>Object</code> may be deliberately created for which this is not true (e.g. by {{jsxref("Object.create", "Object.create(null)")}}), or it may be altered so that this is no longer true (e.g. with {{jsxref("Object.setPrototypeOf")}}).</p>
<p>Changes to the <code>Object</code> prototype object are seen by <strong>all</strong> objects through prototype chaining, unless the properties and methods subject to those changes are overridden further along the prototype chain. This provides a very powerful although potentially dangerous mechanism to override or extend object behavior.</p>
<h2 id="Propriedades">Propriedades</h2>
<dl>
<dt>{{jsxref("Object.prototype.constructor")}}</dt>
<dd>Specifies the function that creates an object's prototype.</dd>
<dt>{{jsxref("Object.prototype.__proto__")}} {{non-standard_inline}}</dt>
<dd>Points to the object which was used as prototype when the object was instantiated.</dd>
<dt>{{jsxref("Object.prototype.__noSuchMethod__")}} {{non-standard_inline}}</dt>
<dd>Allows a function to be defined that will be executed when an undefined object member is called as a method.</dd>
<dt><s class="obsoleteElement">{{jsxref("Object.prototype.count","Object.prototype.__count__")}} {{obsolete_inline}}</s></dt>
<dd><s class="obsoleteElement">Used to return the number of enumerable properties directly on a user-defined object, but has been removed.</s></dd>
<dt><s class="obsoleteElement">{{jsxref("Object.prototype.parent","Object.prototype.__parent__")}} {{obsolete_inline}}</s></dt>
<dd><s class="obsoleteElement">Used to point to an object's context, but has been removed.</s></dd>
</dl>
<h2 id="Métodos">Métodos</h2>
<dl>
<dt>{{jsxref("Object.prototype.__defineGetter__()")}} {{non-standard_inline}} {{deprecated_inline}}</dt>
<dd>Associates a function with a property that, when accessed, executes that function and returns its return value.</dd>
<dt>{{jsxref("Object.prototype.__defineSetter__()")}} {{non-standard_inline}} {{deprecated_inline}}</dt>
<dd>Associates a function with a property that, when set, executes that function which modifies the property.</dd>
<dt>{{jsxref("Object.prototype.__lookupGetter__()")}} {{non-standard_inline}} {{deprecated_inline}}</dt>
<dd>Returns the function associated with the specified property by the {{jsxref("Object.prototype.__defineGetter__()", "__defineGetter__()")}} method.</dd>
<dt>{{jsxref("Object.prototype.__lookupSetter__()")}} {{non-standard_inline}} {{deprecated_inline}}</dt>
<dd>Returns the function associated with the specified property by the {{jsxref("Object.prototype.__defineSetter__()", "__defineSetter__()")}} method.</dd>
<dt>{{jsxref("Object.prototype.hasOwnProperty()")}}</dt>
<dd>Returns a boolean indicating whether an object contains the specified property as a direct property of that object and not inherited through the prototype chain.</dd>
<dt>{{jsxref("Object.prototype.isPrototypeOf()")}}</dt>
<dd>Returns a boolean indicating whether the object this method is called upon is in the prototype chain of the specified object.</dd>
<dt>{{jsxref("Object.prototype.propertyIsEnumerable()")}}</dt>
<dd>Returns a boolean indicating if the internal <a href="/en-US/docs/Web/JavaScript/Data_structures#Properties">ECMAScript [[Enumerable]] attribute</a> is set.</dd>
<dt>{{jsxref("Object.prototype.toSource()")}} {{non-standard_inline}}</dt>
<dd>Returns string containing the source of an object literal representing the object that this method is called upon; you can use this value to create a new object.</dd>
<dt>{{jsxref("Object.prototype.toLocaleString()")}}</dt>
<dd>Calls {{jsxref("Object.toString", "toString()")}}.</dd>
<dt>{{jsxref("Object.prototype.toString()")}}</dt>
<dd>Returns a string representation of the object.</dd>
<dt>{{jsxref("Object.prototype.unwatch()")}} {{non-standard_inline}}</dt>
<dd>Removes a watchpoint from a property of the object.</dd>
<dt>{{jsxref("Object.prototype.valueOf()")}}</dt>
<dd>Returns the primitive value of the specified object.</dd>
<dt>{{jsxref("Object.prototype.watch()")}} {{non-standard_inline}}</dt>
<dd>Adds a watchpoint to a property of the object.</dd>
<dt><s class="obsoleteElement">{{jsxref("Object.prototype.eval()")}} {{obsolete_inline}}</s></dt>
<dd><s class="obsoleteElement">Used to evaluate a string of JavaScript code in the context of the specified object, but has been removed.</s></dd>
</dl>
<h2 id="Exemplos">Exemplos</h2>
<p>When altering the behavior of existing Object.prototype methods, consider injecting code by wrapping your extension before or after the existing logic. For example, this (untested) code will pre-conditionally execute custom logic before the built-in logic or someone else's extension is executed.</p>
<p>When a function is called, the arguments to the call are held in the array-like "variable" <a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments">arguments</a>. For example, in the call "myFn(a, b, c)", the arguments within myFn's body will contain 3 array-like elements corresponding to (a, b, c). When modifying prototypes with hooks, simply pass this & the arguments (the call state) to the current behavior by calling apply() on the function. This pattern can be used for any prototype, such as Node.prototype, Function.prototype, etc.</p>
<pre class="brush: js">var current = Object.prototype.valueOf;
// Since my property "-prop-value" is cross-cutting and isn't always
// on the same prototype chain, I want to modify Object.prototype:
Object.prototype.valueOf = function() {
if (this.hasOwnProperty('-prop-value')) {
return this['-prop-value'];
} else {
// It doesn't look like one of my objects, so let's fall back on
// the default behavior by reproducing the current behavior as best we can.
// The apply behaves like "super" in some other languages.
// Even though valueOf() doesn't take arguments, some other hook may.
return current.apply(this, arguments);
}
}
</pre>
<p>Since JavaScript doesn't exactly have sub-class objects, prototype is a useful workaround to make a “base class” object of certain functions that act as objects. For example:</p>
<pre class="brush: js">var Person = function(name) {
this.name = name;
this.canTalk = true;
};
Person.prototype.greet = function() {
if (this.canTalk) {
console.log('Hi, I am ' + this.name);
}
};
var Employee = function(name, title) {
Person.call(this, name);
this.title = title;
};
Employee.prototype = Object.create(Person.prototype);
Employee.prototype.greet = function() {
if (this.canTalk) {
console.log('Hi, I am ' + this.name + ', the ' + this.title);
}
};
var Customer = function(name) {
Person.call(this, name);
};
Customer.prototype = Object.create(Person.prototype);
var Mime = function(name) {
Person.call(this, name);
this.canTalk = false;
};
Mime.prototype = Object.create(Person.prototype);
var bob = new Employee('Bob', 'Builder');
var joe = new Customer('Joe');
var rg = new Employee('Red Green', 'Handyman');
var mike = new Customer('Mike');
var mime = new Mime('Mime');
bob.greet();
// Hi, I am Bob, the Builder
joe.greet();
// Hi, I am Joe
rg.greet();
// Hi, I am Red Green, the Handyman
mike.greet();
// Hi, I am Mike
mime.greet();
</pre>
<h2 id="Especificações">Especificações</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Especificação</th>
<th scope="col">Estado</th>
<th scope="col">Comentário</th>
</tr>
<tr>
<td>{{SpecName('ES1')}}</td>
<td>{{Spec2('ES1')}}</td>
<td>Initial definition. Implemented in JavaScript 1.0.</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-15.2.3.1', 'Object.prototype')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-object.prototype', 'Object.prototype')}}</td>
<td>{{Spec2('ES6')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-object.prototype', 'Object.prototype')}}</td>
<td>{{Spec2('ESDraft')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="Compatibilidade_de_navegador">Compatibilidade de navegador</h2>
<div>
<p>{{Compat("javascript.builtins.Object.prototype")}}</p>
</div>
<h2 id="Consultar_também">Consultar também</h2>
<ul>
<li><a href="/pt-PT/docs/Learn/JavaScript/Objects">Introdução ao JavaScript Orientado a Objetos</a></li>
</ul>
|
