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JavaScript 中全域物件 Array 是陣列的建構子,陣列是高階、似列表的物件。

建立一個陣列
var fruits = ["Apple", "Banana"];

console.log(fruits.length);
// 2
存取一個陣列項目
var first = fruits[0];
// Apple

var last = fruits[fruits.length - 1];
// Banana
對陣列使用迴圈
fruits.forEach(function (item, index, array) {
  console.log(item, index);
});
// Apple 0
// Banana 1
加入項目至陣列末端
var newLength = fruits.push("Orange");
// ["Apple", "Banana", "Orange"]
移除陣列末端項目
var last = fruits.pop(); // 移除 Orange (from the end)
// ["Apple", "Banana"];
移除陣列前端項目
var first = fruits.shift(); // remove Apple from the front
// ["Banana"];
加入項目至陣列前端
var newLength = fruits.unshift("Strawberry") // add to the front
// ["Strawberry", "Banana"];
陣列中尋找項目的索引
fruits.push("Mango");
// ["Strawberry", "Banana", "Mango"]

var pos = fruits.indexOf("Banana");
// 1
以索引位置移除項目
var removedItem = fruits.splice(pos, 1); // this is how to remove an item
// ["Strawberry", "Mango"]

自索引位置移除項目

var removedItems = fruits.splice(pos, n); // this is how to remove items, n defines the number of items to be removed,
                                          // from that position onward to the end of array.
// let, n = 1;

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

語法

[element0, element1, ..., elementN]
new Array(element0, element1[, ...[, elementN]])
new Array(arrayLength)
elementN
JavaScript 陣列初始化時,是用指定給他的元素,除了以一個參數傳遞給  Array 構造函數的情況,並且參數為一個數字 (見下文) 。注意,這種特殊情況僅適用於以 Array 構造函數建立的 JavaScript  array ,不是用括號語法創建的 array 常數。
arrayLength
如果傳遞給 Array 構造函數的唯一參數,為 0 和 232-1 (含) 之間的整數,這將返回一個新的 JavaScript 陣列,陣列長度設定為這一數字。如果參數是任何其他的數字,這個異常 RangeError  會拋出。

說明

Array ("陣列" 或 "數組") 是類似列表 (list) 的物件 (Object),它們的原型 (Prototype) 擁有方法 (methods) 來執行遍歷和變異操作。JavaScript 陣列的長度 (元素數量) ,以及其元素的類型都不是固定的。由於陣列的長度可以在任何時間改變,並且數據可以存儲在陣列中的非連續位置, JavaScript 陣列是沒有保證是集中的;這取決於工程師如何選擇使用它們。在一般情況,這些是便利特性;但是,如果這些功能都不符合您的特定用途,你可能會考慮使用 typed arrays。

有些人認為 不應該使用關聯數組。而應該使用objects , 即使這麼做會導致警告。 參考輕量級 JavaScript 字典

存取陣列元素

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 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); // 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:

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

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

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 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.

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 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 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:

屬性/元素 說明 範例
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

屬性

For properties available on Array instances, see Properties of Array instances.
Array.length
Array 建構子的長度為 1。
Array.prototype
Allows the addition of properties to all array objects.
Properties inherited from Function:

方法

For methods available on Array instances, see Methods of Array instances.
Array.from()
Creates a new Array instance from an array-like or iterable object.
Array.isArray()
Returns true if a variable is an array, if not false.
Array.of()
Creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments.

Array 實例

All Array instances inherit from Array.prototype. The prototype object of the Array constructor can be modified to affect all Array instances.

屬性

Array.prototype.constructor
Specifies the function that creates an object's prototype.
Array.prototype.length
Reflects the number of elements in an array.
Array.prototype[@@unscopables]
A symbol containing property names to exclude from a with binding scope.

方法

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.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.join()
Joins all elements of an array into a string.
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.
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.

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.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.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.forEach()
Calls a function for each element in the array.
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.some()
Returns true if at least one element in this array satisfies the provided testing function.
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

Array generics are non-standard, deprecated and will get removed in the near future. Note that you can not rely on them cross-browser. However, there is a shim available on GitHub.

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 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]);
  }
}());

範例

範例:建立一個陣列

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.');
}

範例:建立二維陣列

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'));

以下是輸出:

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

使用陣列來以表格顯示多個數值

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

結果會是

0	1	0
1	2	2
2	4	8
3	8	18
4	16	32
5	32	50
6	64	72
7	128	98
8	256	128
9	512	162

(第一欄為 (索引))

技術規格

技術規格 狀態 備註
ECMAScript 1st Edition. Standard Initial definition.
ECMAScript 5.1 (ECMA-262)
The definition of 'Array' in that specification.
Standard 增加的新方法: Array.isArray, indexOf, lastIndexOf, every, some, forEach, map, filter, reduce, reduceRight
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Array' in that specification.
Standard New methods added: Array.from, Array.of, find, findIndex, fill, copyWithin

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