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Array

JavaScript arrays can grow or shrink in size after creation.

var cities = ["Sochi", "New York"];
alert("cities.length=" + cities.length);

var years = new Array(1969, 1970);
years[46] = 2015; //You can add array elements in this way.
alert("years.length=" + years.length);

alert("years=" + years);

for (var idx in years) {
  alert(years[idx]);
}
cities.length=2
years.length=47
years=1969,1970,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,2015
1969
1970
2015

Methods of Array

splice()

Cut specific elements from an array and create a new array with that elements. You can add other elements when creating a new array using splice().

slice()

It returns a new array of parts of the array.

concat()

Combines two or more arrays to return a copy of the combined array.

reverse()

It flips the order of the array.

The concat() and the slice() methods do not change the original array and return the result as a new array.

The JavaScript engine converts the array into a string separated by a comma (,).

var words = new Array('A','B','C','D','E');
var s1 = words.splice(2,2,'c','d');//Remove two elements from index 2 and add 'c' and 'd' at that position 

alert(words);
alert(s1);

var s2 = words.slice(2,4);//Returns a new array from index 2 to index 3 (not including index 4).
alert(s2);
alert(words);
A,B,c,d,E
C,D
c,d
A,B,c,d,E

for .. in

var lang = ["C", "JAVA", "javascript"];
for (var idx in lang) {
  alert(lang[idx]);
}
C
JAVA
javascript

Associative arrays

Associative arrays can not access an element using an index. When you create an associative array, you typically use Object. Associative arrays also automatically adjust in size whenever you add a new element or remove an element.

var account = new Object();

account["accountNo"] = "1111-2222-3333";
account["name"] = "John Doe";
account["balance"] = 30000;

alert(account["name"]);
alert(account.balance);
John Doe
30000

The following shows how to access an element in an associative array.

//Access the getElementsByTagName() element of the associative array document.
document.getElementsByTagName('a');
//Access the element ceil() of the associative array Math.
Math.ceil(175);

The following statement prints all elements of the document object.

for (var property in document) {
  alert(property + ":" + document[property]);
}
location:http://java-school.net/javascript/Array
implementation:[object DOMImplementation]
URL:http://java-school.net/javascript/Array
documentURI:http://java-school.net/javascript/Array
compatMode:CSS1Compat
characterSet:UTF-8
charset:UTF-8
inputEncoding:UTF-8
contentType:text/html
doctype:[object DocumentType]
documentElement:[object HTMLHtmlElement]
xmlEncoding:null
xmlVersion:null
xmlStandalone:false
domain:java-school.net
referrer:
cookie:
lastModified:05/23/2025 00:46:20
readyState:interactive
title:Array
dir:
body:[object HTMLBodyElement]
head:[object HTMLHeadElement]
images:[object HTMLCollection]
embeds:[object HTMLCollection]
plugins:[object HTMLCollection]
links:[object HTMLCollection]
forms:[object HTMLCollection]
scripts:[object HTMLCollection]
currentScript:null
defaultView:[object Window]
designMode:off
onreadystatechange:null
anchors:[object HTMLCollection]
applets:[object HTMLCollection]
fgColor:
linkColor:
vlinkColor:
alinkColor:
bgColor:
all:[object HTMLAllCollection]
scrollingElement:[object HTMLHtmlElement]
onpointerlockchange:null
onpointerlockerror:null
hidden:false
visibilityState:visible
wasDiscarded:false
prerendering:false
featurePolicy:[object FeaturePolicy]
webkitVisibilityState:visible
webkitHidden:false
onbeforecopy:null
onbeforecut:null
onbeforepaste:null
onfreeze:null
onprerenderingchange:null
onresume:null
onsearch:null
onvisibilitychange:null
timeline:[object DocumentTimeline]
fullscreenEnabled:true
fullscreen:false
onfullscreenchange:null
onfullscreenerror:null
webkitIsFullScreen:false
webkitCurrentFullScreenElement:null
webkitFullscreenEnabled:true
webkitFullscreenElement:null
onwebkitfullscreenchange:null
onwebkitfullscreenerror:null
rootElement:null
pictureInPictureEnabled:true
onbeforexrselect:null
onabort:null
onbeforeinput:null
onbeforematch:null
onbeforetoggle:null
onblur:null
oncancel:null
oncanplay:null
oncanplaythrough:null
onchange:null
onclick:null
onclose:null
oncontentvisibilityautostatechange:null
oncontextlost:null
oncontextmenu:null
oncontextrestored:null
oncuechange:null
ondblclick:null
ondrag:null
ondragend:null
ondragenter:null
ondragleave:null
ondragover:null
ondragstart:null
ondrop:null
ondurationchange:null
onemptied:null
onended:null
onerror:null
onfocus:null
onformdata:null
oninput:null
oninvalid:null
onkeydown:null
onkeypress:null
onkeyup:null
onload:null
onloadeddata:null
onloadedmetadata:null
onloadstart:null
onmousedown:null
onmouseenter:null
onmouseleave:null
onmousemove:null
onmouseout:null
onmouseover:null
onmouseup:null
onmousewheel:null
onpause:null
onplay:null
onplaying:null
onprogress:null
onratechange:null
onreset:null
onresize:null
onscroll:null
onsecuritypolicyviolation:null
onseeked:null
onseeking:null
onselect:null
onslotchange:null
onstalled:null
onsubmit:null
onsuspend:null
ontimeupdate:null
ontoggle:null
onvolumechange:null
onwaiting:null
onwebkitanimationend:null
onwebkitanimationiteration:null
onwebkitanimationstart:null
onwebkittransitionend:null
onwheel:null
onauxclick:null
ongotpointercapture:null
onlostpointercapture:null
onpointerdown:null
onpointermove:null
onpointerrawupdate:null
onpointerup:null
onpointercancel:null
onpointerover:null
onpointerout:null
onpointerenter:null
onpointerleave:null
onselectstart:null
onselectionchange:null
onanimationend:null
onanimationiteration:null
onanimationstart:null
ontransitionrun:null
ontransitionstart:null
ontransitionend:null
ontransitioncancel:null
oncopy:null
oncut:null
onpaste:null
children:[object HTMLCollection]
firstElementChild:[object HTMLHtmlElement]
lastElementChild:[object HTMLHtmlElement]
childElementCount:1
activeElement:[object HTMLBodyElement]
styleSheets:[object StyleSheetList]
pointerLockElement:null
fullscreenElement:null
adoptedStyleSheets:
pictureInPictureElement:null
fonts:[object FontFaceSet]
adoptNode:function adoptNode() { [native code] }
append:function append() { [native code] }
captureEvents:function captureEvents() { [native code] }
caretRangeFromPoint:function caretRangeFromPoint() { [native code] }
clear:function clear() { [native code] }
close:function close() { [native code] }
createAttribute:function createAttribute() { [native code] }
createAttributeNS:function createAttributeNS() { [native code] }
createCDATASection:function createCDATASection() { [native code] }
createComment:function createComment() { [native code] }
createDocumentFragment:function createDocumentFragment() { [native code] }
createElement:function createElement() { [native code] }
createElementNS:function createElementNS() { [native code] }
createEvent:function createEvent() { [native code] }
createExpression:function createExpression() { [native code] }
createNSResolver:function createNSResolver() { [native code] }
createNodeIterator:function createNodeIterator() { [native code] }
createProcessingInstruction:function createProcessingInstruction() { [native code] }
createRange:function createRange() { [native code] }
createTextNode:function createTextNode() { [native code] }
createTreeWalker:function createTreeWalker() { [native code] }
elementFromPoint:function elementFromPoint() { [native code] }
elementsFromPoint:function elementsFromPoint() { [native code] }
evaluate:function evaluate() { [native code] }
execCommand:function execCommand() { [native code] }
exitFullscreen:function exitFullscreen() { [native code] }
exitPictureInPicture:function exitPictureInPicture() { [native code] }
exitPointerLock:function exitPointerLock() { [native code] }
getAnimations:function getAnimations() { [native code] }
getElementById:function getElementById() { [native code] }
getElementsByClassName:function getElementsByClassName() { [native code] }
getElementsByName:function getElementsByName() { [native code] }
getElementsByTagName:function getElementsByTagName() { [native code] }
getElementsByTagNameNS:function getElementsByTagNameNS() { [native code] }
getSelection:function getSelection() { [native code] }
hasFocus:function hasFocus() { [native code] }
hasStorageAccess:function hasStorageAccess() { [native code] }
hasUnpartitionedCookieAccess:function hasUnpartitionedCookieAccess() { [native code] }
importNode:function importNode() { [native code] }
open:function open() { [native code] }
prepend:function prepend() { [native code] }
queryCommandEnabled:function queryCommandEnabled() { [native code] }
queryCommandIndeterm:function queryCommandIndeterm() { [native code] }
queryCommandState:function queryCommandState() { [native code] }
queryCommandSupported:function queryCommandSupported() { [native code] }
queryCommandValue:function queryCommandValue() { [native code] }
querySelector:function querySelector() { [native code] }
querySelectorAll:function querySelectorAll() { [native code] }
releaseEvents:function releaseEvents() { [native code] }
replaceChildren:function replaceChildren() { [native code] }
requestStorageAccess:function requestStorageAccess() { [native code] }
requestStorageAccessFor:function requestStorageAccessFor() { [native code] }
startViewTransition:function startViewTransition() { [native code] }
webkitCancelFullScreen:function webkitCancelFullScreen() { [native code] }
webkitExitFullscreen:function webkitExitFullscreen() { [native code] }
write:function write() { [native code] }
writeln:function writeln() { [native code] }
fragmentDirective:[object FragmentDirective]
onscrollend:null
onscrollsnapchange:null
onscrollsnapchanging:null
caretPositionFromPoint:function caretPositionFromPoint() { [native code] }
nodeType:9
nodeName:#document
baseURI:http://java-school.net/javascript/Array
isConnected:true
ownerDocument:null
parentNode:null
parentElement:null
childNodes:[object NodeList]
firstChild:[object DocumentType]
lastChild:[object HTMLHtmlElement]
previousSibling:null
nextSibling:null
nodeValue:null
textContent:null
ELEMENT_NODE:1
ATTRIBUTE_NODE:2
TEXT_NODE:3
CDATA_SECTION_NODE:4
ENTITY_REFERENCE_NODE:5
ENTITY_NODE:6
PROCESSING_INSTRUCTION_NODE:7
COMMENT_NODE:8
DOCUMENT_NODE:9
DOCUMENT_TYPE_NODE:10
DOCUMENT_FRAGMENT_NODE:11
NOTATION_NODE:12
DOCUMENT_POSITION_DISCONNECTED:1
DOCUMENT_POSITION_PRECEDING:2
DOCUMENT_POSITION_FOLLOWING:4
DOCUMENT_POSITION_CONTAINS:8
DOCUMENT_POSITION_CONTAINED_BY:16
DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC:32
appendChild:function appendChild() { [native code] }
cloneNode:function cloneNode() { [native code] }
compareDocumentPosition:function compareDocumentPosition() { [native code] }
contains:function contains() { [native code] }
getRootNode:function getRootNode() { [native code] }
hasChildNodes:function hasChildNodes() { [native code] }
insertBefore:function insertBefore() { [native code] }
isDefaultNamespace:function isDefaultNamespace() { [native code] }
isEqualNode:function isEqualNode() { [native code] }
isSameNode:function isSameNode() { [native code] }
lookupNamespaceURI:function lookupNamespaceURI() { [native code] }
lookupPrefix:function lookupPrefix() { [native code] }
normalize:function normalize() { [native code] }
removeChild:function removeChild() { [native code] }
replaceChild:function replaceChild() { [native code] }
addEventListener:function addEventListener() { [native code] }
dispatchEvent:function dispatchEvent() { [native code] }
removeEventListener:function removeEventListener() { [native code] }

The above example has different results for different browsers. All JavaScript objects are an associative array.

References