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    Array

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    Sumário

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

    Sintaxe

    [element0, element1, ..., elementN]
    new Array(element0, element1, ..., elementN)
    new Array(arrayLength)
    
    element0, element1, ..., elementN
    Um array JavaScript array é inicializado com elementos fornecidos,  exceto no caso onde um argumento único é passado para o construtor the Array e o conntrutor é um número. (Veja abaixo.) Npte que esse caso especial só se aplica para os arrays JavaScript criados com o construtor Array , e não com array literaiscriados com bracket syntax.
    arrayLength
    Se o único argumento passado para o construtor Array é um número inteiro entre 0 and 232-1 (inclusivo), um novo , e vazio array JavaScript  e seu comprimento é definido para aquele número. Se o argumento for qualquer outro número, um RangeError objeção é mostrado.

    Descrição

    Arrays são list-like objects que vem com uma série de  métodos embutidos para realizar operações de travessia e mutação. Nem o tamanho de um array JavaScript nem os tipos de elementos são fixados. Desde que  o tamanho de um array possa crescer ou encolher a qualquer tempo, arrays JavaScript não tem garantia de serem densos. De uma maneira geral, essas são características convenientes; mas se esses recursos não são desejáveis particularmente para seu caso, você pode considerar usar WebGL typed arrays.

    Note that you shouldn't use an array as an associative array. You can use plain objects instead, although doing so comes with its own caveats. See the post Lightweight JavaScript dictionaries with arbitrary keys as an example.

    Accessando elementos array 

    Arrays JavaScript   são indexados a zero; o primeiro elemento de um array está na posição 0, e o último elemento está na  posição equivalente ao valor da propriedade cumprimento/length array menos 1.

    var arr = ["esse é o primeiro elemento", "esse é o segundo elemento"];
    console.log(arr[0]);              // prints "esse é o primeiro elemento"
    console.log(arr[1]);              // prints "esse é o segundo elemento"
    console.log(arr[arr.length - 1]); // prints "esse é o segundo elemento"
    

    Elementos Array são somente propriedades de objetos, da forma que toString é uma propriedade. Contudo, note que tentando acessar o primeiro elemento de um array da seguinte forma irá passar por um erro de sintaxe:

    console.log(arr.0);
    

    Note que não há nada exclusivo a respeito de arrays JavaScript e suas propriedades que causam isso. As propriedades JavaScript que começam com um dígito não podem ser referenciadas com um ponto. Elas necesitam usar notações de sintaxe corretas (bracket notation) para poderem ser acessadas. Por exemplo, se você tivesse um objeto com a propriedade "3d", isso também teria que ser referenciado usando notações de sintaxe corretas (bracket notation) e não somente um ponto. Essa similariedade é exibida nos 2 exemplos de código a seguir:

    var years = [1950, 1960, 1970, 1980, 1990, 2000, 2010];
    try {
      console.log(years.0);
    }
    catch (ex) {
      console.log("Using bracket notation");
      console.log(years[0]);
    }
    
    try {
      renderer.3d.setTexture(model, "character.png");
    }
    catch (ex) {
      console.log("Using bracket notation");
      renderer["3d"].setTexture(model, "character.png");
    }
    

    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] eventually gets coerced into a string by the JavaScript engine, anyway, 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 logs true:

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

    Relationship between length and numerical properties

    A JavaScript array's length property and numerical properties are connected. Several of the built-in array methods (e.g., join, slice, indexOf, etc.) take into account the value of an array's length property when they're called. Other methods (e.g., push, 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 array will grow to a size large enough to accommodate an element at that index, and the engine will update the array's length property accordingly:

    fruits[3] = "mango";
    console.log(fruits[3]);
    console.log(fruits.length); // 4

    Setting the length property, directly, also results in special behavior.

    fruits.length = 10;
    console.log(fruits);        // The array gets padded with undefined
    console.log(fruits.length); // 10
    

    This is explained further on the 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 that provide information about the match. An array is the return value of RegExp.exec, String.match, and 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

    For properties available on Array instances, see Properties of Array instances.

    prototype
    Allows the addition of properties to all objects.
    Properties inherited from Function:

    Methods

    For methods available on Array instances, see Methods of Array instances.
    isArray Requires JavaScript 1.8.5
    Return true if a variable is an array, if not false.

    Array instances

    Array instances inherit from Array.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all JavaScript Array instances.

    Properties

    Array.prototype.constructor
    Specifies the function that creates an object's prototype.
    Array.prototype.length
    Reflects the number of elements in an array.

    Methods

    Mutator methods

    These methods modify the array:

    Array.prototype.copyWithin()
    Copies a sequence of array elements within the array.
    Array.prototype.fill()
    Fills all the elements of an array from a start index to an end index with a static value.
    Array.prototype.pop()
    Removes the last element from an array and returns that element.
    Array.prototype.push()
    Adds one or more elements to the end of an array and returns the new length of the array.
    Array.prototype.reverse()
    Reverses the order of the elements of an array in place — the first becomes the last, and the last becomes the first.
    Array.prototype.shift()
    Removes the first element from an array and returns that element.
    Array.prototype.sort()
    Sorts the elements of an array in place and returns the array.
    Array.prototype.splice()
    Adds and/or removes elements from an array.
    Array.prototype.unshift()
    Adds one or more elements to the front of an array and returns the new length of the array.

    Accessor methods

    These methods do not modify the array and return some representation of the array.

    Array.prototype.concat()
    Returns a new array comprised of this array joined with other array(s) and/or value(s).
    Array.prototype.includes()
    Determines whether an array contains a certain element, returning true or false as appropriate.
    Array.prototype.join()
    Joins all elements of an array into a string.
    Array.prototype.slice()
    Extracts a section of an array and returns a new array.
    Array.prototype.toSource()
    Returns an array literal representing the specified array; you can use this value to create a new array. Overrides the Object.prototype.toSource() method.
    Array.prototype.toString()
    Returns a string representing the array and its elements. Overrides the Object.prototype.toString() method.
    Array.prototype.toLocaleString()
    Returns a localized string representing the array and its elements. Overrides the Object.prototype.toLocaleString() method.
    Array.prototype.indexOf()
    Returns the first (least) index of an element within the array equal to the specified value, or -1 if none is found.
    Array.prototype.lastIndexOf()
    Returns the last (greatest) index of an element within the array equal to the specified value, or -1 if none is found.

    Iteration methods

    Several methods take as arguments functions to be called back while processing the array. When these methods are called, the length of the array is sampled, and any element added beyond this length from within the callback is not visited. Other changes to the array (setting the value of or deleting an element) may affect the results of the operation if the method visits the changed element afterwards. While the specific behavior of these methods in such cases is well-defined, you should not rely upon it so as not to confuse others who might read your code. If you must mutate the array, copy into a new array instead.

    Array.prototype.forEach()
    Calls a function for each element in the array.
    Array.prototype.entries()
    Returns a new Array Iterator object that contains the key/value pairs for each index in the array.
    Array.prototype.every()
    Returns true if every element in this array satisfies the provided testing function.
    Array.prototype.some()
    Returns true if at least one element in this array satisfies the provided testing function.
    Array.prototype.filter()
    Creates a new array with all of the elements of this array for which the provided filtering function returns true.
    Array.prototype.find()
    Returns the found value in the array, if an element in the array satisfies the provided testing function or undefined if not found.
    Array.prototype.findIndex()
    Returns the found index in the array, if an element in the array satisfies the provided testing function or -1 if not found.
    Array.prototype.keys()
    Returns a new Array Iterator that contains the keys for each index in the array.
    Array.prototype.map()
    Creates a new array with the results of calling a provided function on every element in this array.
    Array.prototype.reduce()
    Apply a function against an accumulator and each value of the array (from left-to-right) as to reduce it to a single value.
    Array.prototype.reduceRight()
    Apply a function against an accumulator and each value of the array (from right-to-left) as to reduce it to a single value.
    Array.prototype.values()
    Returns a new Array Iterator object that contains the values for each index in the array.
    Array.prototype[@@iterator]()
    Returns a new Array Iterator object that contains the values for each index in the array.

    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))
      alert("The string '" + str + "' contains only letters!");
    

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

    if (Array.every(isLetter, str))
      alert("The string '" + str + "' contains only letters!");
    

    Generics are also available on 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:

    /*globals define*/
    // Assumes Array extras already present (one may use shims 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', 'isArray'
            ],
            methodCount = methods.length,
            assignArrayGeneric = function (methodName) {
                var method = Array.prototype[methodName];
                Array[methodName] = function (arg1) {
                    return method.apply(arg1, Array.prototype.slice.call(arguments, 1));
                };
            };
    
        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 = new Array();
    msgArray[0] = "Hello";
    msgArray[99] = "world";
    
    if (msgArray.length == 100)
       print("The length is 100.");
    

    Example: Creating a two-dimensional array

    The following creates 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']];
    print(board.join('\n') + '\n\n');
    
    // Move King's Pawn forward 2
    board[4][4] = board[6][4];
    board[6][4] = ' ';
    print(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
    

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Etiquetas do documento e colaboradores

    Contributors to this page: Sheppy, teoli, xhximenes, euconectei
    Última atualização por: euconectei,
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