Revision 520221 of Array

  • Revision slug: Web/JavaScript/Reference/Global_Objects/Array
  • Revision title: Array
  • Revision id: 520221
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  • Creator: charmander
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  • Comment It doesn’t make sense to show examples of syntax errors inside try blocks.
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{{JSRef("Global_Objects", "Array")}}

Summary

The JavaScript Array global object is a constructor for arrays, which are high-level, list-like objects.

Syntax

[element0, element1, ..., elementN]
new Array(element0, element1, ..., elementN)
new Array(arrayLength)
element0, element1, ..., elementN
A JavaScript array is initialized with the given elements, except in the case where a single argument is passed to the Array constructor and that argument is a number. (See below.) Note that this special case only applies to JavaScript arrays created with the Array constructor, not array literals created with the bracket syntax.
arrayLength
If the only argument passed to the Array constructor is an integer between 0 and 232-1 (inclusive), this returns a new JavaScript array with length set to that number. If the argument is any other number, a {{jsxref("Global_Objects/RangeError", "RangeError")}} exception is thrown.

Description

Arrays are list-like objects whose prototype has methods to perform traversal and mutation operations. Neither the length of a JavaScript array nor the types of its elements are fixed. Since an array's size length grow or shrink at any time, JavaScript arrays are not guaranteed to be dense. In general, these are convenient characteristics; but if these features are not desirable for your particular use, you might consider using typed arrays.

Some people think that you shouldn't use an array as an associative array. In any case, you can use plain {{jsxref("Global_Objects/Object", "objects")}} instead, although doing so comes with its own caveats. See the post Lightweight JavaScript dictionaries with arbitrary keys as an example.

Accessing array elements

JavaScript arrays are zero-indexed: the first element of an array is at index 0, and the last element is at the index equal to the value of the array's {{jsxref("Array.length", "length")}} property minus 1.

var arr = ["this is the first element", "this is the second element"];
console.log(arr[0]);              // prints "this is the first element"
console.log(arr[1]);              // prints "this is the second element"
console.log(arr[arr.length - 1]); // prints "this is the second element"

Array elements are object properties in the same way that toString is a property, but trying to access an element of an array as follows throws a syntax error, because the property name is not valid:

console.log(arr.0);

There is nothing special about JavaScript arrays and their properties that causes this. JavaScript properties that begin with a digit cannot be referenced with dot notation; and must be accessed using bracket notation. For example, if you had an object with a property named "3d", it can only be referenced using bracket notation. E.g.:

var years = [1950, 1960, 1970, 1980, 1990, 2000, 2010];
console.log(years.0); // a syntax error
console.log(years[0]); // works properly
renderer.3d.setTexture(model, "character.png"); // a syntax error
renderer["3d"].setTexture(model, "character.png"); // works properly

Note that in the 3d example, "3d" had to be quoted. It's possible to quote the JavaScript array indexes as well (e.g., years["2"] instead of years[2]), although it's not necessary. The 2 in years[2] is coerced into a string by the JavaScript engine through an implicit toString conversion. It is for this reason that "2" and "02" would refer to two different slots on the years object and the following example could be true:

console.log(years["2"] != years["02"]);

Similarly, object properties which happen to be reserved words(!) can only be accessed as string literals in bracket notation:

var promise = {'var'  : 'text',
               'array': [1, 2, 3, 4] }

console.log(promise['array'])

Relationship between length and numerical properties

A JavaScript array's {{jsxref("Array.length", "length")}} property and numerical properties are connected. Several of the built-in array methods (e.g., {{jsxref("Array.join", "join")}}, {{jsxref("Array.slice", "slice")}}, {{jsxref("Array.indexOf", "indexOf")}}, etc.) take into account the value of an array's length property when they're called. Other methods (e.g., {{jsxref("Array.push", "push")}}, {{jsxref("Array.splice", "splice")}}, etc.) also result in updates to an array's length property.

var fruits = [];
fruits.push("banana", "apple", "peach");

console.log(fruits.length); // 3

When setting a property on a JavaScript array when the property is a valid array index and that index is outside the current bounds of the array, the engine will update the array's length property accordingly:

fruits[5] = "mango";
console.log(fruits[5]); // "mango"
console.log(Object.keys(fruits));  // ["0", "1", "2", "5"]
console.log(fruits.length); // 6

Increasing the length property does not create additional elements.

fruits.length = 10;
console.log(Object.keys(fruits)); // ["0", "1", "2", "5"]
console.log(fruits.length); // 10

Decreasing the length property does, however, delete elements.

fruits.length = 2;
console.log(Object.keys(fruits)); // ["0", "1"]
console.log(fruits.length); // 2
This is explained further on the {{jsxref("Array.length")}} page.

Creating an array using the result of a match

The result of a match between a regular expression and a string can create a JavaScript array. This array has properties and elements which provide information about the match. Such an array is returned by {{jsxref("RegExp.exec")}}, {{jsxref("String.match")}}, and {{jsxref("String.replace")}}. To help explain these properties and elements, look at the following example and then refer to the table below:

// Match one d followed by one or more b's followed by one d
// Remember matched b's and the following d
// Ignore case

var myRe = /d(b+)(d)/i;
var myArray = myRe.exec("cdbBdbsbz");

The properties and elements returned from this match are as follows:

Property/Element Description Example
input A read-only property that reflects the original string against which the regular expression was matched. cdbBdbsbz
index A read-only property that is the zero-based index of the match in the string. 1
[0] A read-only element that specifies the last matched characters. dbBd
[1], ...[n] Read-only elements that specify the parenthesized substring matches, if included in the regular expression. The number of possible parenthesized substrings is unlimited. [1]: bB
[2]: d

Properties

{{ Js_see_prototype("Array", "Properties") }}
Array.length
The Array constructor's length property whose value is 1.
{{jsxref("Array.prototype")}}
Allows the addition of properties to all array objects.
{{ jsOverrides("Function", "Properties", "prototype") }}

Methods

{{ Js_see_prototype("Array", "Methods") }}
{{jsxref("Array.isArray()")}}
Returns true if a variable is an array, if not false.
{{jsxref("Array.of()")}} {{experimental_inline}}
Creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments.

Array instances

All Array instances inherit from {{jsxref("Array.prototype")}}. The prototype object of the Array constructor can be modified to affect all Array instances.

Properties

{{page('/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Properties')}}

Methods

Mutator methods

{{ page('en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Mutator_methods') }}

Accessor methods

{{ page('en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Accessor_methods') }}

Iteration methods

{{ page('en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Iteration_methods') }}

Array generic methods

Sometimes you would like to apply array methods to strings or other array-like objects (such as function arguments). By doing this, you treat a string as an array of characters (or otherwise treat a non-array as an array). For example, in order to check that every character in the variable str is a letter, you would write:

function isLetter(character) {
  return character >= "a" && character <= "z";
}

if (Array.prototype.every.call(str, isLetter)) {
    console.log("The string '" + str + "' contains only letters!");
}

This notation is rather wasteful and JavaScript 1.6 introduced a generic shorthand:

if (Array.every(isLetter, str)) {
    console.log("The string '" + str + "' contains only letters!");
}

Generics are also available on {{jsxref("Global_Objects/String", "String")}}.

These are currently not part of ECMAScript standards (though the ES6 Array.from() can be used to achieve this). The following is a shim to allow its use in all browsers:

// Assumes Array extras already present (one may use polyfills for these as well)
(function () {
    'use strict';

    var i,
        // We could also build the array of methods with the following, but the
        //   getOwnPropertyNames() method is non-shimable:
        // Object.getOwnPropertyNames(Array).filter(function (methodName) {
        //     return typeof Array[methodName] === 'function'});
        methods = [
            'join', 'reverse', 'sort', 'push', 'pop', 'shift', 'unshift',
            'splice', 'concat', 'slice', 'indexOf', 'lastIndexOf',
            'forEach', 'map', 'reduce', 'reduceRight', 'filter',
            'some', 'every'
        ],
        methodCount = methods.length,
        assignArrayGeneric = function (methodName) {
            if (!Array[methodName]) {
                var method = Array.prototype[methodName];
                if (typeof method === 'function') {
                    Array[methodName] = function () {
                        return method.call.apply(method, arguments);
                    };
                }
            }
        };

    for (i = 0; i < methodCount; i++) {
        assignArrayGeneric(methods[i]);
    }
}());

Examples

Example: Creating an array

The following example creates an array, msgArray, with a length of 0, then assigns values to msgArray[0] and msgArray[99], changing the length of the array to 100.

var msgArray = [];
msgArray[0] = "Hello";
msgArray[99] = "world";

if (msgArray.length === 100) {
    console.log("The length is 100.");
}

Example: Creating a two-dimensional array

The following creates a chess board as a two dimensional array of strings. The first move is made by copying the 'p' in (6,4) to (4,4). The old position 6,4 is made blank.

var board = [ 
    ['R','N','B','Q','K','B','N','R'],
    ['P','P','P','P','P','P','P','P'],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    ['p','p','p','p','p','p','p','p'],
    ['r','n','b','q','k','b','n','r'] ];

console.log(board.join('\n') + '\n\n');

// Move King's Pawn forward 2
board[4][4] = board[6][4];
board[6][4] = ' ';
console.log(board.join('\n'));

Here is the output:

R,N,B,Q,K,B,N,R
P,P,P,P,P,P,P,P
 , , , , , , , 
 , , , , , , , 
 , , , , , , , 
 , , , , , , , 
p,p,p,p,p,p,p,p
r,n,b,q,k,b,n,r

R,N,B,Q,K,B,N,R
P,P,P,P,P,P,P,P
 , , , , , , , 
 , , , , , , , 
 , , , ,p, , , 
 , , , , , , , 
p,p,p,p, ,p,p,p
r,n,b,q,k,b,n,r

Specifications

Specification Status Comment
ECMAScript 1st Edition. Standard Initial definition.
{{SpecName('ES5.1', '#sec-15.4', 'Array')}} {{Spec2('ES5.1')}} New methods added: Array.isArray, indexOf, lastIndexOf, every, some, forEach, map, filter, reduce, reduceRight  
{{SpecName('ES6', '#sec-array-objects', 'Array')}} {{Spec2('ES6')}} New methods added: Array.from, Array.of, find, findIndex, fill, copyWithin

Browser compatibility

{{ CompatibilityTable() }}

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }}
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }}

See also

Revision Source

<p>{{JSRef("Global_Objects", "Array")}}</p>
<h2 id="Summary">Summary</h2>
<p>The JavaScript <strong><code>Array</code></strong> global object is a constructor for arrays, which are high-level, list-like objects.</p>
<h2 id="Syntax">Syntax</h2>
<pre class="syntaxbox">
[<var>element0</var>, <var>element1</var>, ..., <var>elementN</var>]
new Array(<em>element0</em>, <em>element1</em>, ..., <em>elementN</em>)
new Array(<em>arrayLength</em>)
</pre>
<dl>
 <dt>
  <code><var>element0</var>, <var>element1</var>, ..., <var>elementN</var> </code></dt>
 <dd>
  A JavaScript array is initialized with the given elements, except in the case where a single argument is passed to the <code>Array</code> constructor and that argument is a number. (See below.) Note that this special case only applies to JavaScript arrays created with the <code>Array</code> constructor, not array literals created with the bracket syntax.</dd>
 <dt>
  <code><var>arrayLength</var></code></dt>
 <dd>
  If the only argument passed to the <code>Array</code> constructor is an integer between 0 and 2<sup>32</sup>-1 (inclusive), this returns a new JavaScript array with length set to that number. If the argument is any other number, a {{jsxref("Global_Objects/RangeError", "RangeError")}} exception is thrown.</dd>
</dl>
<h2 id="Description">Description</h2>
<p>Arrays are list-like objects whose prototype has methods to perform traversal and mutation operations. Neither the length of a JavaScript array nor the types of its elements are fixed. Since an array's size length grow or shrink at any time, JavaScript arrays are not guaranteed to be dense. In general, these are convenient characteristics; but if these features are not desirable for your particular use, you might consider using typed arrays.</p>
<p>Some people think that <a class="external" href="http://www.andrewdupont.net/2006/05/18/javascript-associative-arrays-considered-harmful/">you shouldn't use an array as an associative array</a>. In any case, you can use plain {{jsxref("Global_Objects/Object", "objects")}} instead, although doing so comes with its own caveats. See the post <a class="external" href="http://www.less-broken.com/blog/2010/12/lightweight-javascript-dictionaries.html" title="http://monogatari.doukut.su/2010/12/lightweight-javascript-dictionaries.html">Lightweight JavaScript dictionaries with arbitrary keys</a> as an example.</p>
<h3 id="Accessing_array_elements">Accessing array elements</h3>
<p>JavaScript arrays are zero-indexed: the first element of an array is at index <code>0</code>, and the last element is at the index equal to the value of the array's {{jsxref("Array.length", "length")}} property minus 1.</p>
<pre class="brush: js">
var arr = ["this is the first element", "this is the second element"];
console.log(arr[0]);              // prints "this is the first element"
console.log(arr[1]);              // prints "this is the second element"
console.log(arr[arr.length - 1]); // prints "this is the second element"
</pre>
<p>Array elements are object properties in the same way that <code>toString</code> is a property, but trying to access an element of an array as follows throws a syntax error, because the property name is not valid:</p>
<pre class="brush: js">
console.log(arr.0);
</pre>
<p>There is nothing special about JavaScript arrays and their properties that causes this. JavaScript properties that begin with a digit cannot be referenced with dot notation; and must be accessed using bracket notation. For example, if you had an object with a property named "3d", it can only be referenced using bracket notation. E.g.:</p>
<pre class="brush: js">
var years = [1950, 1960, 1970, 1980, 1990, 2000, 2010];
console.log(years.0); // a syntax error
console.log(years[0]); // works properly
</pre>
<pre class="brush: js">
renderer.3d.setTexture(model, "character.png"); // a syntax error
renderer["3d"].setTexture(model, "character.png"); // works properly
</pre>
<p>Note that in the <code>3d</code> example, "<code>3d</code>" had to be quoted. It's possible to quote the JavaScript array indexes as well (e.g., <code>years["2"]</code> instead of <code>years[2]</code>), although it's not necessary. The 2 in <code>years[2]</code> is coerced into a string by the JavaScript engine through an implicit <code>toString</code> conversion. It is for this reason that <code>"2"</code> and <code>"02"</code> would refer to two different slots on the <code>years</code> object and the following example could be <code>true</code>:</p>
<pre class="brush: js">
console.log(years["2"] != years["02"]);
</pre>
<p id="Relationship_between_length_and_numerical_properties">Similarly, object properties which happen to be reserved words(!) can only be accessed as string literals in bracket notation:</p>
<pre class="brush: js">
var promise = {'var'  : 'text',
               'array': [1, 2, 3, 4] }

console.log(promise['array'])</pre>
<h3 id="Relationship_between_length_and_numerical_properties">Relationship between <code>length</code> and numerical properties</h3>
<p>A JavaScript array's {{jsxref("Array.length", "length")}} property and numerical properties are connected. Several of the built-in array methods (e.g., {{jsxref("Array.join", "join")}}, {{jsxref("Array.slice", "slice")}}, {{jsxref("Array.indexOf", "indexOf")}}, etc.) take into account the value of an array's <code>length</code> property when they're called. Other methods (e.g., {{jsxref("Array.push", "push")}}, {{jsxref("Array.splice", "splice")}}, etc.) also result in updates to an array's <code>length</code> property.</p>
<pre class="brush: js">
var fruits = [];
fruits.push("banana", "apple", "peach");

console.log(fruits.length); // 3</pre>
<p>When setting a property on a JavaScript array when the property is a valid array index and that index is outside the current bounds of the array, the engine will update the array's <code>length</code> property accordingly:</p>
<pre class="brush: js">
fruits[5] = "mango";
console.log(fruits[5]); // "mango"
console.log(Object.keys(fruits));  // ["0", "1", "2", "5"]
console.log(fruits.length); // 6</pre>
<p>Increasing the&nbsp;<code style="font-size: 14px;">length</code>&nbsp;property does not create additional elements.</p>
<pre class="brush: js" style="font-size: 14px;">
fruits.length = 10;
console.log(Object.keys(fruits)); // ["0", "1", "2", "5"]
console.log(fruits.length); // 10
</pre>
<div>
 <p>Decreasing the&nbsp;<code style="font-size: 14px;">length</code>&nbsp;property does, however, delete elements.</p>
 <pre class="brush: js" style="font-size: 14px;">
fruits.length = 2;
console.log(Object.keys(fruits)); // ["0", "1"]
console.log(fruits.length); // 2
</pre>
 <div>
  <span style="line-height: 1.572;">This is explained further on the {{jsxref("Array.length")}}</span><span style="line-height: 1.572;"> page.</span></div>
</div>
<h3 id="Creating_an_array_using_the_result_of_a_match">Creating an array using the result of a match</h3>
<p>The result of a match between a regular expression and a string can create a JavaScript array. This array has properties and elements which provide information about the match. Such an array is returned by {{jsxref("RegExp.exec")}}, {{jsxref("String.match")}}, and {{jsxref("String.replace")}}. To help explain these properties and elements, look at the following example and then refer to the table below:</p>
<pre class="brush: js">
// Match one d followed by one or more b's followed by one d
// Remember matched b's and the following d
// Ignore case

var myRe = /d(b+)(d)/i;
var myArray = myRe.exec("cdbBdbsbz");
</pre>
<p>The properties and elements returned from this match are as follows:</p>
<table class="fullwidth-table">
 <tbody>
  <tr>
   <td class="header">Property/Element</td>
   <td class="header">Description</td>
   <td class="header">Example</td>
  </tr>
  <tr>
   <td><code>input</code></td>
   <td>A read-only property that reflects the original string against which the regular expression was matched.</td>
   <td>cdbBdbsbz</td>
  </tr>
  <tr>
   <td><code>index</code></td>
   <td>A read-only property that is the zero-based index of the match in the string.</td>
   <td>1</td>
  </tr>
  <tr>
   <td><code>[0]</code></td>
   <td>A read-only element that specifies the last matched characters.</td>
   <td>dbBd</td>
  </tr>
  <tr>
   <td><code>[1], ...[n]</code></td>
   <td>Read-only elements that specify the parenthesized substring matches, if included in the regular expression. The number of possible parenthesized substrings is unlimited.</td>
   <td>[1]: bB<br />
    [2]: d</td>
  </tr>
 </tbody>
</table>
<h2 id="Properties">Properties</h2>
<div>
 {{ Js_see_prototype("Array", "Properties") }}</div>
<dl>
 <dt>
  Array.length</dt>
 <dd>
  The <code>Array</code> constructor's length property whose value is 1.</dd>
 <dt>
  {{jsxref("Array.prototype")}}</dt>
 <dd>
  Allows the addition of properties to all array objects.</dd>
</dl>
<div>
 {{ jsOverrides("Function", "Properties", "prototype") }}</div>
<h2 id="Methods">Methods</h2>
<div>
 {{ Js_see_prototype("Array", "Methods") }}</div>
<dl>
 <dt>
  {{jsxref("Array.isArray()")}}</dt>
 <dd>
  Returns true if a variable is an array, if not false.</dd>
 <dt>
  {{jsxref("Array.of()")}} {{experimental_inline}}</dt>
 <dd>
  Creates a new <code>Array</code> instance with a variable number of arguments, regardless of number or type of the arguments.</dd>
</dl>
<h2 id="Array_instances"><code>Array</code> instances</h2>
<p>All <code>Array</code> instances inherit from {{jsxref("Array.prototype")}}. The prototype object of the <code>Array</code> constructor can be modified to affect all <code>Array</code> instances.</p>
<h3 id="Methods_of_array_instances" name="Methods_of_array_instances">Properties</h3>
<div>
 {{page('/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Properties')}}</div>
<h3 id="Methods_of_array_instances" name="Methods_of_array_instances">Methods</h3>
<h4 id="Mutator_methods">Mutator methods</h4>
<div>
 {{ page('en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Mutator_methods') }}</div>
<div>
 <h4 id="Accessor_methods">Accessor methods</h4>
 <p>{{ page('en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Accessor_methods') }}</p>
 <h4 id="Iteration_methods">Iteration methods</h4>
 <p>{{ page('en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype', 'Iteration_methods') }}</p>
</div>
<h2 id="Array_generic_methods"><code>Array</code> generic methods</h2>
<p>Sometimes you would like to apply array methods to strings or other array-like objects (such as function <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/arguments" title="https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Functions_and_function_scope/arguments"><code>arguments</code></a>). By doing this, you treat a string as an array of characters (or otherwise treat a non-array as an array). For example, in order to check that every character in the variable <var>str</var> is a letter, you would write:</p>
<pre class="brush: js">
function isLetter(character) {
  return character &gt;= "a" &amp;&amp; character &lt;= "z";
}

if (Array.prototype.every.call(str, isLetter)) {
    console.log("The string '" + str + "' contains only letters!");
}</pre>
<p>This notation is rather wasteful and JavaScript 1.6 introduced a generic shorthand:</p>
<pre class="brush: js">
if (Array.every(isLetter, str)) {
    console.log("The string '" + str + "' contains only letters!");
}</pre>
<p><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#String_generic_methods" title="https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String#String_generic_methods">Generics</a> are also available on {{jsxref("Global_Objects/String", "String")}}.</p>
<p>These are currently not part of ECMAScript standards (though the ES6 <a href="https://github.com/monolithed/ECMAScript-6" title="https://github.com/monolithed/ECMAScript-5"><code>Array.from()</code></a> can be used to achieve this). The following is a shim to allow its use in all browsers:</p>
<pre class="brush: js">
// Assumes Array extras already present (one may use polyfills for these as well)
(function () {
&nbsp;&nbsp;&nbsp; 'use strict';

&nbsp;&nbsp;&nbsp; var i,
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // We could also build the array of methods with the following, but the
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //&nbsp;&nbsp; getOwnPropertyNames() method is non-shimable:
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // Object.getOwnPropertyNames(Array).filter(function (methodName) {
        //     return typeof Array[methodName] === 'function'});
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; methods = [
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'join', 'reverse', 'sort', 'push', 'pop', 'shift', 'unshift',
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'splice', 'concat', 'slice', 'indexOf', 'lastIndexOf',
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'forEach', 'map', 'reduce', 'reduceRight', 'filter',
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'some', 'every'
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ],
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; methodCount = methods.length,
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; assignArrayGeneric = function (methodName) {
            if (!Array[methodName]) {
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; var method = Array.prototype[methodName];
                if (typeof method === 'function') {
    &nbsp;&nbsp;&nbsp;&nbsp;    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Array[methodName] = function () {
&nbsp;&nbsp;&nbsp;&nbsp;    &nbsp;&nbsp;&nbsp;&nbsp;    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return method.call.apply(method, arguments);
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;    &nbsp;&nbsp;&nbsp;     };
                }
            }
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; };

&nbsp;&nbsp;&nbsp; for (i = 0; i &lt; methodCount; i++) {
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; assignArrayGeneric(methods[i]);
&nbsp;&nbsp;&nbsp; }
}());</pre>
<h2 id="Examples">Examples</h2>
<h3 id="Example.3A_Creating_an_array">Example: Creating an array</h3>
<p>The following example creates an array, <code>msgArray</code>, with a length of 0, then assigns values to <code>msgArray[0]</code> and <code>msgArray[99]</code>, changing the length of the array to 100.</p>
<pre class="brush: js">
var msgArray = [];
msgArray[0] = "Hello";
msgArray[99] = "world";

if (msgArray.length === 100) {
    console.log("The length is 100.");
}</pre>
<h3 id="Example.3A_Creating_a_two-dimensional_array">Example: Creating a two-dimensional array</h3>
<p>The following creates a chess board as a two dimensional array of strings. The first move is made by copying the 'p' in (6,4) to (4,4). The old position 6,4 is made blank.</p>
<pre class="brush: js">
var board = [ 
    ['R','N','B','Q','K','B','N','R'],
    ['P','P','P','P','P','P','P','P'],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    [' ',' ',' ',' ',' ',' ',' ',' '],
    ['p','p','p','p','p','p','p','p'],
    ['r','n','b','q','k','b','n','r'] ];

console.log(board.join('\n') + '\n\n');

// Move King's Pawn forward 2
board[4][4] = board[6][4];
board[6][4] = ' ';
console.log(board.join('\n'));
</pre>
<p>Here is the output:</p>
<pre class="eval">
R,N,B,Q,K,B,N,R
P,P,P,P,P,P,P,P
 , , , , , , , 
 , , , , , , , 
 , , , , , , , 
 , , , , , , , 
p,p,p,p,p,p,p,p
r,n,b,q,k,b,n,r

R,N,B,Q,K,B,N,R
P,P,P,P,P,P,P,P
 , , , , , , , 
 , , , , , , , 
 , , , ,p, , , 
 , , , , , , , 
p,p,p,p, ,p,p,p
r,n,b,q,k,b,n,r
</pre>
<h2 id="Specifications">Specifications</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>ECMAScript 1st Edition.</td>
   <td>Standard</td>
   <td>Initial definition.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-15.4', 'Array')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td>New methods added: Array.isArray, <span>indexOf, <span>lastIndexOf,&nbsp;</span><span>every, <span>some, forEach, map, filter, reduce, reduceRight </span>&nbsp;</span> </span></td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-array-objects', 'Array')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>New methods added: Array.from, Array.of, find, findIndex, fill, copyWithin</td>
  </tr>
 </tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</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="See_also" name="See_also">See also</h2>
<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Guide/Working_with_Objects#Indexing_object_properties" title="JavaScript/Guide/Working_with_objects#Indexing_object_properties">JavaScript Guide: "Indexing object properties"</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/Guide/Predefined_Core_Objects#Array_Object">JavaScript Guide: "Predefined Core Objects: Array Object"</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/1.7#Array_comprehensions" title="New_in_JavaScript_1.7#Array_comprehensions">New in JavaScript 1.7: Array comprehensions</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/New_in_JavaScript/1.6#Array_extras" title="New_in_JavaScript_1.6#Array_extras">New in JavaScript 1.6: Array extras</a></li>
 <li><a href="https://github.com/plusdude/array-generics" title="https://github.com/plusdude/array-generics">Polyfill for JavaScript 1.8.5 Array Generics and ECMAScript 5 Array Extras</a></li>
 <li><a href="/en-US/docs/JavaScript_typed_arrays" title="JavaScript_typed_arrays">Typed Arrays</a></li>
</ul>
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