--- title: Array slug: Web/JavaScript/Reference/Global_Objects/Array tags: - Array - Class - Exemplo - Global Objects - JavaScript - Referencia - 'l10n:priority' translation_of: Web/JavaScript/Reference/Global_Objects/Array ---

A classe de JavaScript Array é um objecto global que é utilizado na construção de matrizes; que são objectos de alto nível, semelhantes a listas.

Descrição

Arrays são objectos em forma de lista, cujo protótipo tem métodos para realizar operações de travessia e mutação. Nem o comprimento de uma array JavaScript nem os tipos dos seus elementos são fixos. Uma vez que o comprimento de uma array pode mudar a qualquer momento, e os dados podem ser armazenados em locais não contíguos da array, não é garantido que uma array JavaScript seja densa; isto depende de como o programador opta por usá-las. Em geral, estas são características convenientes; mas se estas características não forem desejáveis para seu uso particular, você pode considerar o uso de arrays tipadas.

Uma array não pode utilizar strings como índices de elementos (como num {{InterWiki("wikipedia", "Vetor_associativo", "array associativa")}}), deve utilizar números inteiros. A definição ou acesso através de não-inteiros usando notação de parênteses (ou notação de pontos) não definirá ou recuperará um elemento da própria lista da array, mas definirá ou acessará uma variável associada à coleção de propriedades dessa array. As propriedades da array e a lista de elementos do mesmo são separadas, e as operações de translação e mutação da array não podem ser aplicadas a essas propriedades com nome.

Criar uma Array

var fruits = ['Apple', 'Banana'];

console.log(fruits.length);
// 2

Aceder (através de índice) item da Array

var first = fruits[0];
// Apple

var last = fruits[fruits.length - 1];
// Banana

Loop over an Array

fruits.forEach(function(item, index, array) {
  console.log(item, index);
});
// Apple 0
// Banana 1

Adicionar um item ao fim da Array

var newLength = fruits.push('Orange');
// ["Apple", "Banana", "Orange"]

Remover um item do fim da Array

var last = fruits.pop(); // remove Orange (from the end)
// ["Apple", "Banana"];

Remover um item do início da Array

var first = fruits.shift(); // remove Apple from the front
// ["Banana"];

Adicionar um item ao início da Array

var newLength = fruits.unshift('Strawberry') // add to the front
// ["Strawberry", "Banana"];

Encontrar o índice dum item na Array

fruits.push('Mango');
// ["Strawberry", "Banana", "Mango"]

var pos = fruits.indexOf('Banana');
// 1

Remover um item pela posição do índice

var removedItem = fruits.splice(pos, 1); // this is how to remove an item

// ["Strawberry", "Mango"]

Remover items pela posição do índice

var vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot'];
console.log(vegetables);
// ["Cabbage", "Turnip", "Radish", "Carrot"]

var pos = 1, n = 2;

var removedItems = vegetables.splice(pos, n);
// this is how to remove items, n defines the number of items to be removed,
// from that position(pos) onward to the end of array.

console.log(vegetables);
// ["Cabbage", "Carrot"] (the original array is changed)

console.log(removedItems);
// ["Turnip", "Radish"]

Copiar uma Array

var shallowCopy = fruits.slice(); // this is how to make a copy
// ["Strawberry"]

Como aceder a elementos da array

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]);              // logs 'this is the first element'
console.log(arr[1]);              // logs 'this is the second element'
console.log(arr[arr.length - 1]); // logs '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); // a syntax error

There is nothing special about JavaScript arrays and the properties that cause 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(but it can be accessed by dot notation in firefox 40.0a2 at least):

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

console.log(promise['var']);

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 {{jsxref("Array.length", "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 {{jsxref("Array.length", "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 {{jsxref("Array.length", "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 {{jsxref("Array.length", "length")}}.

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

Decreasing the {{jsxref("Array.length", "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

Array.length: The Array constructor's length property whose value is 1.
{{jsxref("Array.@@species", "get Array[@@species]")}}: The constructor function that is used to create derived objects.
{{jsxref("Array.prototype")}}: Allows the addition of properties to all array objects.

Methods

{{jsxref("Array.from()")}}: Creates a new Array instance from an array-like or iterable object.
{{jsxref("Array.isArray()")}}: Returns true if a variable is an array, if not false.
{{jsxref("Array.of()")}}: 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

Array generics are non-standard, deprecated and will get removed in the near future.

Sometimes you would like to apply array methods to strings or other array-like objects (such as function {{jsxref("Functions/arguments", "arguments", "", 1)}}). 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(str, isLetter)) {
  console.log("The string '" + str + "' contains only letters!");
}

{{jsxref("Global_Objects/String", "Generics", "#String_generic_methods", 1)}} are also available on {{jsxref("String")}}.

These are not part of ECMAScript standards and they are not supported by non-Gecko browsers. As a standard alternative, you can convert your object to a proper array using {{jsxref("Array.from()")}}; although that method may not be supported in old browsers:

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

Examples

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.');
}

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

Using an array to tabulate a set of values

values = [];
for (var x = 0; x < 10; x++){
 values.push([
  2 ** x,
  2 * x ** 2
 ])
};
console.table(values)

Results in

(First column is the (index))

Specifications

Specification	Status	Comment
{{SpecName('ES1')}}	{{Spec2('ES1')}}	Initial definition.
{{SpecName('ES5.1', '#sec-15.4', 'Array')}}	{{Spec2('ES5.1')}}	New methods added: {{jsxref("Array.isArray")}}, {{jsxref("Array.prototype.indexOf", "indexOf")}}, {{jsxref("Array.prototype.lastIndexOf", "lastIndexOf")}}, {{jsxref("Array.prototype.every", "every")}}, {{jsxref("Array.prototype.some", "some")}}, {{jsxref("Array.prototype.forEach", "forEach")}}, {{jsxref("Array.prototype.map", "map")}}, {{jsxref("Array.prototype.filter", "filter")}}, {{jsxref("Array.prototype.reduce", "reduce")}}, {{jsxref("Array.prototype.reduceRight", "reduceRight")}}
{{SpecName('ES6', '#sec-array-objects', 'Array')}}	{{Spec2('ES6')}}	New methods added: {{jsxref("Array.from")}}, {{jsxref("Array.of")}}, {{jsxref("Array.prototype.find", "find")}}, {{jsxref("Array.prototype.findIndex", "findIndex")}}, {{jsxref("Array.prototype.fill", "fill")}}, {{jsxref("Array.prototype.copyWithin", "copyWithin")}}
{{SpecName('ESDraft', '#sec-array-objects', 'Array')}}	{{Spec2('ESDraft')}}	New method added: {{jsxref("Array.prototype.includes()")}}

Descrição

Como aceder a elementos da array

Relationship between `length` and numerical properties

Creating an array using the result of a match

Properties

Methods

`Array` instances

Properties

Methods

Mutator methods

Accessor methods

Iteration methods

`Array` generic methods

Examples

Creating an array

Creating a two-dimensional array

Using an array to tabulate a set of values

Specifications

Compatibilidade de Navegadores

See also

Descrição

Como aceder a elementos da array

Relationship between length and numerical properties

Creating an array using the result of a match

Properties

Methods

Array instances

Properties

Methods

Mutator methods

Accessor methods

Iteration methods

Array generic methods

Examples

Creating an array

Creating a two-dimensional array

Using an array to tabulate a set of values

Specifications

Compatibilidade de Navegadores

See also

Relationship between `length` and numerical properties

`Array` instances

`Array` generic methods