The JavaScript Array object is a global object that is used in the construction of arrays; which are high-level, list-like objects.
Create an Array
var fruits = ["Apple", "Banana"]; console.log(fruits.length); // 2
Access (index into) an Array item
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
Add to the end of an Array
var newLength = fruits.push("Orange");
// ["Apple", "Banana", "Orange"]
Remove from the end of an Array
var last = fruits.pop(); // remove Orange (from the end) // ["Apple", "Banana"];
Remove from the front of an Array
var first = fruits.shift(); // remove Apple from the front // ["Banana"];
Add to the front of an Array
var newLength = fruits.unshift("Strawberry") // add to the front
// ["Strawberry", "Banana"];
Find the index of an item in the Array
fruits.push("Mango");
// ["Strawberry", "Banana", "Mango"]
var pos = fruits.indexOf("Banana");
// 1
Remove an item by Index Position
var removedItem = fruits.splice(pos, 1); // this is how to remove an item // ["Strawberry", "Mango"]
Copy an Array
var shallowCopy = fruits.slice(); // this is how to make a copy // ["Strawberry", "Mango"]
Syntax
[element0, element1, ..., elementN]
new Array(element0, element1[, ...[, elementN]])
new Array(arrayLength)elementN- A JavaScript array is initialized with the given elements, except in the case where a single argument is passed to the
Arrayconstructor and that argument is a number (see the arrayLength parameter below).Note that this special case only applies to JavaScript arrays created with theArrayconstructor, not array literals created with the bracket syntax. arrayLength- If the only argument passed to the
Arrayconstructor 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("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 length can change at any time, and data can be stored at non-contiguous locations in the array, JavaScript arrays are not guaranteed to be dense; this depends on how the programmer chooses to use them. 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]); // 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['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 {{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
Arrayconstructor'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
Arrayinstance 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
Arrayinstance 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
Methods
Mutator methods
Accessor methods
Iteration methods
Array generic methods
Array generics are non-standard, deprecated and will get removed 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 {{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 (though the ES6 {{jsxref("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', 'find', 'findIndex', 'entries', 'keys',
'values', 'copyWithin', 'includes'
],
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
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
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()")}} |
Browser compatibility
| 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}} |