path: root/files/pt-pt/web/javascript/data_structures/index.html

---
title: Tipos de dados de JavaScript e estruturas de dados
slug: Web/JavaScript/Estruturas_de_dados
tags:
  - JavaScript
  - Principiante
  - Tipos
translation_of: Web/JavaScript/Data_structures
---
<div>{{jsSidebar("More")}}</div>

<p>Programming languages all have built-in data structures, but these often differ from one language to another. This article attempts to list the built-in data structures available in JavaScript and what properties they have; these can be used to build other data structures. When possible, comparisons with other languages are drawn.</p>

<h2 id="Digitação_dinâmica">Digitação dinâmica</h2>

<p>JavaScript is a <em>loosely typed</em> or a <em>dynamic</em> language. Variables in JavaScript are not directly associated with any particular value type, and any variable can be assigned (and re-assigned)  values of all types:</p>

<pre class="brush: js">var foo = 42;    // foo is now a Number
var foo = 'bar'; // foo is now a String
var foo = true;  // foo is now a Boolean
</pre>

<h2 id="Tipos_de_dados">Tipos de dados</h2>

<p>The latest ECMAScript standard defines seven data types:</p>

<ul>
 <li>Six data types that are {{Glossary("Primitive", "primitives")}}:
  <ul>
   <li>{{Glossary("Boolean")}}</li>
   <li>{{Glossary("Null")}}</li>
   <li>{{Glossary("Undefined")}}</li>
   <li>{{Glossary("Number")}}</li>
   <li>{{Glossary("String")}}</li>
   <li>{{Glossary("Symbol")}} (new in ECMAScript 6)</li>
  </ul>
 </li>
 <li>and {{Glossary("Object")}}</li>
</ul>

<h2 id="Valores_primitivos">Valores primitivos</h2>

<p>All types except objects define immutable values (values, which are incapable of being changed). For example and unlike to C, Strings are immutable. We refer to values of these types as "primitive values".</p>

<h3 id="Tipo_booleano">Tipo booleano</h3>

<p>Boolean represents a logical entity and can have two values: <code>true</code>, and <code>false</code>.</p>

<h3 id="Tipo_Null">Tipo <em>Null</em></h3>

<p>The Null type has exactly one value: <code>null</code>. See {{jsxref("null")}} and {{Glossary("Null")}} for more details.</p>

<h3 id="Tipo_indefinido">Tipo indefinido</h3>

<p>A variable that has not been assigned a value has the value <code>undefined</code>. See {{jsxref("undefined")}} and {{Glossary("Undefined")}} for more details.</p>

<h3 id="Tipo_número">Tipo número</h3>

<p>According to the ECMAScript standard, there is only one number type: the <a href="http://en.wikipedia.org/wiki/Double_precision_floating-point_format">double-precision 64-bit binary format IEEE 754 value</a> (number between -(2<sup>53</sup> -1) and 2<sup>53</sup> -1). <strong>There is no specific type for integers</strong>. In addition to being able to represent floating-point numbers, the number type has three symbolic values: <code>+Infinity</code>, <code>-Infinity</code>, and <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN"><code>NaN</code></a> (not-a-number).</p>

<p>To check for the largest available value or smallest available value within <code>+/-Infinity</code>, you can use the constants {{jsxref("Number.MAX_VALUE")}} or {{jsxref("Number.MIN_VALUE")}} and starting with ECMAScript 6, you are also able to check if a number is in the double-precision floating-point number range using {{jsxref("Number.isSafeInteger()")}} as well as {{jsxref("Number.MAX_SAFE_INTEGER")}} and {{jsxref("Number.MIN_SAFE_INTEGER")}}. Beyond this range, integers in JavaScript are not safe anymore and will be a double-precision floating point approximation of the value.</p>

<p>The number type has only one integer that has two representations: 0 is represented as -0 and +0. ("0" is an alias for +0). In the praxis, this has almost no impact. For example <code>+0 === -0</code> is <code>true</code>. However, you are able to notice this when you divide by zero:</p>

<pre class="brush: js">&gt; 42 / +0
Infinity
&gt; 42 / -0
-Infinity
</pre>

<p>Although a number often represents only its value, JavaScript provides <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators" title="en/JavaScript/Reference/Operators/Bitwise_Operators">some binary operators</a>. These can be used to represent several Boolean values within a single number using <a class="external" href="http://en.wikipedia.org/wiki/Mask_%28computing%29">bit masking</a>. However, this is usually considered a bad practice, since JavaScript offers other means to represent a set of Booleans (like an array of Booleans or an object with Boolean values assigned to named properties). Bit masking also tends to make code more difficult to read, understand, and maintain. It may be necessary to use such techniques in very constrained environments, like when trying to cope with the storage limitation of local storage or in extreme cases when each bit over the network counts. This technique should only be considered when it is the last measure that can be taken to optimize size.</p>

<h3 id="Tipo_string">Tipo <em>string</em></h3>

<p>JavaScript's {{jsxref("Global_Objects/String", "String")}} type is used to represent textual data. It is a set of "elements" of 16-bit unsigned integer values. Each element in the String occupies a position in the String. The first element is at index 0, the next at index 1, and so on. The length of a String is the number of elements in it.</p>

<p>Unlike in languages like C, JavaScript strings are immutable. This means that once a string is created, it is not possible to modify it. However, it is still possible to create another string based on an operation on the original string. For example:</p>

<ul>
 <li>A substring of the original by picking individual letters or using {{jsxref("String.substr()")}}.</li>
 <li>A concatenation of two strings using the concatenation operator (<code>+</code>) or {{jsxref("String.concat()")}}.</li>
</ul>

<h4 id="Beware_of_stringly-typing_your_code!">Beware of "stringly-typing" your code!</h4>

<p>It can be tempting to use strings to represent complex data. Doing this comes with short-term benefits:</p>

<ul>
 <li>It is easy to build complex strings with concatenation.</li>
 <li>Strings are easy to debug (what you see printed is always what is in the string).</li>
 <li>Strings are the common denominator of a lot of APIs (<a href="/en-US/docs/Web/API/HTMLInputElement" title="HTMLInputElement">input fields</a>, <a href="/en-US/docs/Storage" title="Storage">local storage</a> values, {{ domxref("XMLHttpRequest") }} responses when using <code>responseText</code>, etc.) and it can be tempting to only work with strings.</li>
</ul>

<p>With conventions, it is possible to represent any data structure in a string. This does not make it a good idea. For instance, with a separator, one could emulate a list (while a JavaScript array would be more suitable). Unfortunately, when the separator is used in one of the "list" elements, then, the list is broken. An escape character can be chosen, etc. All of this requires conventions and creates an unnecessary maintenance burden.</p>

<p>Use strings for textual data. When representing complex data, parse strings and use the appropriate abstraction.</p>

<h3 id="Tipo_símbolo">Tipo símbolo</h3>

<p>Symbols are new to JavaScript in ECMAScript Edition 6. A Symbol is a <strong>unique</strong> and <strong>immutable</strong> primitive value and may be used as the key of an Object property (see below). In some programming languages, Symbols are called atoms. For more details see {{Glossary("Symbol")}} and the {{jsxref("Symbol")}} object wrapper in JavaScript.</p>

<h2 id="Objetos">Objetos</h2>

<p>In computer science, an object is a value in memory which is possibly referenced by an {{Glossary("Identifier", "identifier")}}.</p>

<h3 id="Propriedades">Propriedades</h3>

<p>In JavaScript, objects can be seen as a collection of properties. With the <a href="/en-US/docs/Web/JavaScript/Guide/Values,_variables,_and_literals#Object_literals">object literal syntax</a>, a limited set of properties are initialized; then properties can be added and removed. Property values can be values of any type, including other objects, which enables building complex data structures. Properties are identified using key values. A key value is either a String or a Symbol value.</p>

<p>There are two types of object properties which have certain attributes: The data property and the accessor property.</p>

<h4 id="Data_property">Data property</h4>

<p>Associates a key with a value and has the following attributes:</p>

<table class="standard-table">
 <caption>Attributes of a data property</caption>
 <tbody>
  <tr>
   <th>Attribute</th>
   <th>Type</th>
   <th>Description</th>
   <th>Default value</th>
  </tr>
  <tr>
   <td>[[Value]]</td>
   <td>Any JavaScript type</td>
   <td>The value retrieved by a get access of the property.</td>
   <td>undefined</td>
  </tr>
  <tr>
   <td>[[Writable]]</td>
   <td>Boolean</td>
   <td>If <code>false</code>, the property's [[Value]] can't be changed.</td>
   <td>false</td>
  </tr>
  <tr>
   <td>[[Enumerable]]</td>
   <td>Boolean</td>
   <td>If <code>true</code>, the property will be enumerated in <a href="/en-US/docs/Web/JavaScript/Reference/Statements/for...in">for...in</a> loops. See also <a href="/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">Enumerability and ownership of properties</a></td>
   <td>false</td>
  </tr>
  <tr>
   <td>[[Configurable]]</td>
   <td>Boolean</td>
   <td>If <code>false</code>, the property can't be deleted and attributes other than [[Value]] and [[Writable]] can't be changed.</td>
   <td>false</td>
  </tr>
 </tbody>
</table>

<table class="standard-table">
 <caption>Obsolete attributes (as of ECMAScript 3, renamed in ECMAScript 5)</caption>
 <tbody>
  <tr>
   <th>Attribute</th>
   <th>Type</th>
   <th>Description</th>
  </tr>
  <tr>
   <td>Read-only</td>
   <td>Boolean</td>
   <td>Reversed state of the ES5 [[Writable]] attribute.</td>
  </tr>
  <tr>
   <td>DontEnum</td>
   <td>Boolean</td>
   <td>Reversed state of the ES5 [[Enumerable]] attribute.</td>
  </tr>
  <tr>
   <td>DontDelete</td>
   <td>Boolean</td>
   <td>Reversed state of the ES5 [[Configurable]] attribute.</td>
  </tr>
 </tbody>
</table>

<h4 id="Accessor_property">Accessor property</h4>

<p>Associates a key with one or two accessor functions (get and set) to retrieve or store a value and has the following attributes:</p>

<table class="standard-table">
 <caption>Attributes of an accessor property</caption>
 <tbody>
  <tr>
   <th>Attribute</th>
   <th>Type</th>
   <th>Description</th>
   <th>Default value</th>
  </tr>
  <tr>
   <td>[[Get]]</td>
   <td>Function object or undefined</td>
   <td>The function is called with an empty argument list and retrieves the property value whenever a get access to the value is performed. See also <a href="/en-US/docs/Web/JavaScript/Reference/Operators/get"><code>get</code></a>.</td>
   <td>undefined</td>
  </tr>
  <tr>
   <td>[[Set]]</td>
   <td>Function object or undefined</td>
   <td>The function is called with an argument that contains the assigned value and is executed whenever a specified property is attempted to be changed. See also <a href="/en-US/docs/Web/JavaScript/Reference/Operators/set"><code>set</code></a>.</td>
   <td>undefined</td>
  </tr>
  <tr>
   <td>[[Enumerable]]</td>
   <td>Boolean</td>
   <td>If <code>true</code>, the property will be enumerated in <a href="/en-US/docs/Web/JavaScript/Reference/Statements/for...in">for...in</a> loops.</td>
   <td>false</td>
  </tr>
  <tr>
   <td>[[Configurable]]</td>
   <td>Boolean</td>
   <td>If <code>false</code>, the property can't be deleted and can't be changed to a data property.</td>
   <td>false</td>
  </tr>
 </tbody>
</table>

<div class="note">
<p><strong>Note: </strong>Attribute is usually used by JavaScript engine, so you can't directly access it(see more about <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty">Object.defineProperty()</a>).That's why the attribute is put in double square brackets instead of single.</p>
</div>

<h3 id="Objetos_Normal_e_funções">Objetos "Normal", e funções</h3>

<p>A JavaScript object is a mapping between keys and values. Keys are strings (or {{jsxref("Symbol")}}s) and values can be anything. This makes objects a natural fit for <a class="external" href="http://en.wikipedia.org/wiki/Hash_table">hashmaps</a>.</p>

<p>Functions are regular objects with the additional capability of being callable.</p>

<h3 id="Dates"><em>Dates</em></h3>

<p>When representing dates, the best choice is to use the built-in <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date"><code>Date</code> utility</a> in JavaScript.</p>

<h3 id="Coleções_indexadas_Arrays_e_Arrays_digitados">Coleções indexadas: <em>Arrays </em>e <em>Arrays </em>digitados</h3>

<p><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Array" title="Array">Arrays</a> are regular objects for which there is a particular relationship between integer-key-ed properties and the 'length' property. Additionally, arrays inherit from <code>Array.prototype</code> which provides to them a handful of convenient methods to manipulate arrays. For example, <code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf" title="en/JavaScript/Reference/Global_Objects/Array/indexOf">indexOf</a></code> (searching a value in the array) or <code><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Array/push" title="en/JavaScript/Reference/Global_Objects/Array/push">push</a></code> (adding an element to the array), etc. This makes Arrays a perfect candidate to represent lists or sets.</p>

<p><a href="/en-US/docs/Web/JavaScript/Typed_arrays">Typed Arrays</a> are new to JavaScript with ECMAScript Edition 6 and present an array-like view of an underlying binary data buffer. The following table helps you to find the equivalent C data types:</p>

<p>{{page("/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray", "TypedArray_objects", "", 0, 3)}}</p>

<h3 id="Keyed_collections_Maps_Sets_WeakMaps_WeakSets">Keyed collections: Maps, Sets, WeakMaps, WeakSets</h3>

<p>These data structures take object references as keys and are introduced in ECMAScript Edition 6. {{jsxref("Set")}} and {{jsxref("WeakSet")}} represent a set of objects, while {{jsxref("Map")}} and {{jsxref("WeakMap")}} associate a value to an object. The difference between Maps and WeakMaps is that in the former, object keys can be enumerated over. This allows garbage collection optimizations in the latter case.</p>

<p>One could implement Maps and Sets in pure ECMAScript 5. However, since objects cannot be compared (in the sense of "less than" for instance), look-up performance would necessarily be linear. Native implementations of them (including WeakMaps) can have look-up performance that is approximately logarithmic to constant time.</p>

<p>Usually, to bind data to a DOM node, one could set properties directly on the object or use <code>data-*</code> attributes. This has the downside that the data is available to any script running in the same context. Maps and WeakMaps make it easy to privately bind data to an object.</p>

<h3 id="Structured_data_JSON">Structured data: JSON</h3>

<p>JSON (JavaScript Object Notation) is a lightweight data-interchange format, derived from JavaScript but used by many programming languages. JSON builds universal data structures. See {{Glossary("JSON")}} and {{jsxref("JSON")}} for more details.</p>

<h3 id="More_objects_in_the_standard_library">More objects in the standard library</h3>

<p>JavaScript has a standard library of built-in objects. Please have a look at the <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects">reference</a> to find out about more objects.</p>

<h2 id="Determining_types_using_the_typeof_operator">Determining types using the <code>typeof</code> operator</h2>

<p>The <code>typeof</code> operator can help you to find the type of your variable. Please read the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof">reference page</a> for more details and edge cases.</p>

<h2 id="Especificações">Especificações</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES1')}}</td>
   <td>{{Spec2('ES1')}}</td>
   <td>Initial definition.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-8', 'Types')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-ecmascript-data-types-and-values', 'ECMAScript Data Types and Values')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-ecmascript-data-types-and-values', 'ECMAScript Data Types and Values')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="Consulte_também">Consulte também</h2>

<ul>
 <li><a class="link-https" href="https://github.com/nzakas/computer-science-in-javascript/">Nicholas Zakas collection of common data structure and common algorithms in JavaScript.</a></li>
 <li><a href="https://github.com/monmohan/DataStructures_In_Javascript" title="https://github.com/monmohan/DataStructures_In_Javascript">Search Tre(i)es implemented in JavaScript</a></li>
</ul>