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Array

Core object
Implemented in	JavaScript 1.1, NES 2.0
ECMA version	ECMA-262

Created by

The Array object constructor:

new Array(arrayLength)
new Array(element0, element1, ..., elementN)

An array literal:

[element0, element1, ..., elementN]

JavaScript 1.2 when you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag:

new Array(element0, element1, ..., elementN)

Parameters

arrayLength	The initial length of the array. You can access this value using the `length` property. If the value specified is not a number, an array of length 1 is created, with the first element having the specified value. The maximum length allowed for an array is 4,294,967,295.
elementN	A list of values for the array's elements. When this form is specified, the array is initialized with the specified values as its elements, and the array's `length` property is set to the number of arguments.

Description

An array is an ordered set of values associated with a single variable name.

The following example creates an Array object with an array literal; the coffees array contains three elements and a length of three:

coffees = ["French Roast", "Columbian", "Kona"]

You can construct a dense array of two or more elements starting with index 0 if you define initial values for all elements. A dense array is one in which each element has a value. The following code creates a dense array with three elements:

myArray = new Array("Hello", myVar, 3.14159)

Indexing an array. You index an array by its ordinal number. For example, assume you define the following array:

myArray = new Array("Wind","Rain","Fire")

You then refer to the first element of the array as myArray[0] and the second element of the array as myArray[1].

Specifying a single parameter. When you specify a single numeric parameter with the Array constructor, you specify the initial length of the array. The following code creates an array of five elements:

billingMethod = new Array(5)

The behavior of the Array constructor depends on whether the single parameter is a number.

If the value specified is a number, the constructor converts the number to an unsigned, 32-bit integer and generates an array with the length property (size of the array) set to the integer. The array initially contains no elements, even though it might have a non-zero length.

If the value specified is not a number, an array of length 1 is created, with the first element having the specified value.

The following code creates an array of length 25, then assigns values to the first three elements:

musicTypes = new Array(25)
musicTypes[0] = "R&B"
musicTypes[1] = "Blues"
musicTypes[2] = "Jazz"

When you specify a single parameter with the Array constructor in JavaScript 1.2, the behavior depends on whether you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag:

If you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag, a single-element array is returned. For example, new Array(5) creates a one-element array with the first element being 5. A constructor with a single parameter acts in the same way as a multiple parameter constructor. You cannot specify the length property of an Array using a constructor with one parameter.

If you do not specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag, you specify the initial length of the array as with other JavaScript versions.

Increasing the array length indirectly. An array's length increases if you assign a value to an element higher than the current length of the array. The following code creates an array of length 0, then assigns a value to element 99. This changes the length of the array to 100.

colors = new Array()
colors[99] = "midnightblue"

Creating an array using the result of a match. The result of a match between a regular expression and a string can create an 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:

<SCRIPT LANGUAGE="JavaScript1.2">
//Match one d followed by one or more b's followed by one d
//Remember matched b's and the following d
//Ignore case

myRe=/d(b+)(d)/i;
myArray = myRe.exec("cdbBdbsbz");

</SCRIPT>

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

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

Backward Compatibility

JavaScript 1.1 and earlier. When you specify a single parameter with the Array constructor, you specify the initial length of the array. The following code creates an array of five elements:

billingMethod = new Array(5)

JavaScript 1.0. You must index an array by its ordinal number; for example myArray[0].

Property Summary

Property Description
constructor
Specifies the function that creates an object's prototype.

index
For an array created by a regular expression match, the zero-based index of the match in the string.

input
For an array created by a regular expression match, reflects the original string against which the regular expression was matched.

length
An integer that specifies the number of elements in an array.

prototype
Allows the addition of properties to all objects.

Property	Description
`constructor`	Specifies the function that creates an object's prototype.
`index`	For an array created by a regular expression match, the zero-based index of the match in the string.
`input`	For an array created by a regular expression match, reflects the original string against which the regular expression was matched.
`length`	An integer that specifies the number of elements in an array.
`prototype`	Allows the addition of properties to all objects.

Method Summary

Method Description
concat
Joins two arrays and returns a new array.

join
Joins all elements of an array into a string.

pop
Removes the last element from an array and returns that element.

push
Adds one or more elements to the end of an array and returns the last element added to the array.

reverse
Transposes the elements of an array: the first array element becomes the last and the last becomes the first.

shift
Removes the first element from an array and returns that element

slice
Extracts a section of an array and returns a new array.

splice
Adds and/or removes elements from an array.

sort
Sorts the elements of an array.

toString
Returns a string representing the array and its elements. Overrides the Object.toString method.

unshift
Adds one or more elements to the front of an array and returns the new length of the array.

valueOf
Returns the primitive value of the array. Overrides the Object.valueOf method.

Method	Description
`concat`	Joins two arrays and returns a new array.
`join`	Joins all elements of an array into a string.
`pop`	Removes the last element from an array and returns that element.
`push`	Adds one or more elements to the end of an array and returns the last element added to the array.
`reverse`	Transposes the elements of an array: the first array element becomes the last and the last becomes the first.
`shift`	Removes the first element from an array and returns that element
`slice`	Extracts a section of an array and returns a new array.
`splice`	Adds and/or removes elements from an array.
`sort`	Sorts the elements of an array.
`toString`	Returns a string representing the array and its elements. Overrides the `Object.toString` method.
`unshift`	Adds one or more elements to the front of an array and returns the new length of the array.
`valueOf`	Returns the primitive value of the array. Overrides the `Object.valueOf` method.

In addition, this object inherits the watch and unwatch methods from Object.

Examples

Example 1. 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.

msgArray = new Array()
msgArray[0] = "Hello"
msgArray[99] = "world"
// The following statement is true,
// because defined msgArray[99] element.
if (msgArray.length == 100) 
   myVar="The length is 100."

Example 2: Two-dimensional array. The following code creates a two-dimensional array and assigns the results to myVar.

myVar="Multidimensional array test; "
a = new Array(4)
for (i=0; i < 4; i++) {
   a[i] = new Array(4)
   for (j=0; j < 4; j++) {
      a[i][j] = "["+i+","+j+"]"
   }
}
for (i=0; i < 4; i++) {
   str = "Row "+i+":"
   for (j=0; j < 4; j++) {
      str += a[i][j]
   }
   myVar += str +"; "
}

This example assigns the following string to myVar (line breaks are used here for readability):

Multidimensional array test;
Row 0:[0,0][0,1][0,2][0,3];
Row 1:[1,0][1,1][1,2][1,3];
Row 2:[2,0][2,1][2,2][2,3];
Row 3:[3,0][3,1][3,2][3,3];

concat

Joins two arrays and returns a new array.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

concat(arrayName2, arrayName3, ..., arrayNameN)

Description

concat does not alter the original arrays, but returns a "one level deep" copy that contains copies of the same elements combined from the original arrays. Elements of the original arrays are copied into the new array as follows:

Object references (and not the actual object): concat copies object references into the new array. Both the original and new array refer to the same object. If a referenced object changes, the changes are visible to both the new and original arrays.

Strings and numbers (not String and Number objects): concat copies strings and numbers into the new array. Changes to the string or number in one array does not affect the other arrays.

If a new element is added to either array, the other array is not affected.

The following code concatenates two arrays:

alpha=new Array("a","b","c")
numeric=new Array(1,2,3)
alphaNumeric=alpha.concat(numeric) // creates array ["a","b","c",1,2,3]

The following code concatenates three arrays:

num1=[1,2,3]
num2=[4,5,6]
num3=[7,8,9]
nums=num1.concat(num2,num3) // creates array [1,2,3,4,5,6,7,8,9]

index

For an array created by a regular expression match, the zero-based index of the match in the string.

Property of	`Array`
Static
Implemented in	JavaScript 1.2, NES 3.0

input

For an array created by a regular expression match, reflects the original string against which the regular expression was matched.

Property of	`Array`
Static
Implemented in	JavaScript 1.2, NES 3.0

join

Joins all elements of an array into a string.

Method of	`Array`
Implemented in	JavaScript 1.1, NES 2.0
ECMA version	ECMA-262

Syntax

join(separator)

Parameters

separator

Specifies a string to separate each element of the array. The separator is converted to a string if necessary. If omitted, the array elements are separated with a comma.

Description

The string conversions of all array elements are joined into one string.

Examples

The following example creates an array, a, with three elements, then joins the array three times: using the default separator, then a comma and a space, and then a plus.

a = new Array("Wind","Rain","Fire")
myVar1=a.join()      // assigns "Wind,Rain,Fire" to myVar1
myVar2=a.join(", ")  // assigns "Wind, Rain, Fire" to myVar1
myVar3=a.join(" + ") // assigns "Wind + Rain + Fire" to myVar1

length

An integer that specifies the number of elements in an array.

Property of	`Array`
Implemented in	JavaScript 1.1, NES 2.0
ECMA version	ECMA-262

Description

You can set the length property to truncate an array at any time. When you extend an array by changing its length property, the number of actual elements does not increase; for example, if you set length to 3 when it is currently 2, the array still contains only 2 elements.

Examples

In the following example, the getChoice function uses the length property to iterate over every element in the musicType array. musicType is a select element on the musicForm form.

function getChoice() {
   for (var i = 0; i < document.musicForm.musicType.length; i++) {
      if (document.musicForm.musicType.options[i].selected == true) {
         return document.musicForm.musicType.options[i].text
      }
   }
}

The following example shortens the array statesUS to a length of 50 if the current length is greater than 50.

if (statesUS.length > 50) {
   statesUS.length=50
}

pop

Removes the last element from an array and returns that element. This method changes the length of the array.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

pop()

Example

The following code creates the myFish array containing four elements, then removes its last element.

myFish = ["angel", "clown", "mandarin", "surgeon"];
popped = myFish.pop();

prototype

Represents the prototype for this class. You can use the prototype to add properties or methods to all instances of a class. For information on prototypes, see Function.prototype.

Property of	`Array`
Implemented in	JavaScript 1.1, NES 2.0
ECMA version	ECMA-262

push

Adds one or more elements to the end of an array and returns the last element added to the array. This method changes the length of the array.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

push(element1, ..., elementN)

Parameters

element1, ...,
elementN

The elements to add to the end of the array.

Description

The behavior of the push method is analogous to the push function in Perl 4. Note that this behavior is different in Perl 5.

Example

The following code creates the myFish array containing two elements, then adds two elements to it. After the code executes, pushed contains "lion".

myFish = ["angel", "clown"];
pushed = myFish.push("drum", "lion");

reverse

Transposes the elements of an array: the first array element becomes the last and the last becomes the first.

Method of	`Array`
Implemented in	JavaScript 1.1, NES 2.0
ECMA version	ECMA-262

Syntax

reverse()

Description

The reverse method transposes the elements of the calling array object.

Examples

The following example creates an array myArray, containing three elements, then reverses the array.

myArray = new Array("one", "two", "three")
myArray.reverse()

This code changes myArray so that:

myArray[0] is "three"
myArray[1] is "two"
myArray[2] is "one"

shift

Removes the first element from an array and returns that element. This method changes the length of the array.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

shift()

Example

The following code displays the myFish array before and after removing its first element. It also displays the removed element:

myFish = ["angel", "clown", "mandarin", "surgeon"];
document.writeln("myFish before: " + myFish);
shifted = myFish.shift();
document.writeln("myFish after: " + myFish);
document.writeln("Removed this element: " + shifted);

This example displays the following:

myFish before: ["angel", "clown", "mandarin", "surgeon"]
myFish after: ["clown", "mandarin", "surgeon"]
Removed this element: angel

slice

Extracts a section of an array and returns a new array.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

slice(begin[,end])

Parameters

begin

Zero-based index at which to begin extraction.

end

Zero-based index at which to end extraction:

slice extracts up to but not including end. slice(1,4) extracts the second element through the fourth element (elements indexed 1, 2, and 3)
As a negative index, end indicates an offset from the end of the sequence. slice(2,-1) extracts the third element through the second to last element in the sequence.
If end is omitted, slice extracts to the end of the sequence.

Description

slice does not alter the original array, but returns a new "one level deep" copy that contains copies of the elements sliced from the original array. Elements of the original array are copied into the new array as follows:

For object references (and not the actual object), slice copies object references into the new array. Both the original and new array refer to the same object. If a referenced object changes, the changes are visible to both the new and original arrays.

For strings and numbers (not String and Number objects), slice copies strings and numbers into the new array. Changes to the string or number in one array does not affect the other array.

If a new element is added to either array, the other array is not affected.

Example

In the following example, slice creates a new array, newCar, from myCar. Both include a reference to the object myHonda. When the color of myHonda is changed to purple, both arrays reflect the change.

<SCRIPT LANGUAGE="JavaScript1.2">

//Using slice, create newCar from myCar.
myHonda = {color:"red",wheels:4,engine:{cylinders:4,size:2.2}} 
myCar = [myHonda, 2, "cherry condition", "purchased 1997"] 
newCar = myCar.slice(0,2)

//Write the values of myCar, newCar, and the color of myHonda 
// referenced from both arrays.
document.write("myCar = " + myCar + "<BR>")
document.write("newCar = " + newCar + "<BR>") 
document.write("myCar[0].color = " + myCar[0].color + "<BR>") 
document.write("newCar[0].color = " + newCar[0].color + "<BR><BR>")

//Change the color of myHonda.
myHonda.color = "purple"
document.write("The new color of my Honda is " + myHonda.color + "<BR><BR>")

//Write the color of myHonda referenced from both arrays.
document.write("myCar[0].color = " + myCar[0].color + "<BR>") 
document.write("newCar[0].color = " + newCar[0].color + "<BR>")

</SCRIPT>

This script writes:

myCar = [{color:"red", wheels:4, engine:{cylinders:4, size:2.2}}, 2,
   "cherry condition", "purchased 1997"] 
newCar = [{color:"red", wheels:4, engine:{cylinders:4, size:2.2}}, 2] 
myCar[0].color = red newCar[0].color = red 
The new color of my Honda is purple 
myCar[0].color = purple 
newCar[0].color = purple

sort

Sorts the elements of an array.

Method of

Array

Implemented in

JavaScript 1.1, NES 2.0

JavaScript 1.2: modified behavior.

ECMA version

ECMA-262

Syntax

sort(compareFunction)

Parameters

compareFunction

Specifies a function that defines the sort order. If omitted, the array is sorted lexicographically (in dictionary order) according to the string conversion of each element.

Description

If compareFunction is not supplied, elements are sorted by converting them to strings and comparing strings in lexicographic ("dictionary" or "telephone book," not numerical) order. For example, "80" comes before "9" in lexicographic order, but in a numeric sort 9 comes before 80.

If compareFunction is supplied, the array elements are sorted according to the return value of the compare function. If a and b are two elements being compared, then:

If compareFunction(a, b) is less than 0, sort b to a lower index than a.

If compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements.

If compareFunction(a, b) is greater than 0, sort b to a higher index than a.

So, the compare function has the following form:

function compare(a, b) {
   if (a is less than b by some ordering criterion)
      return -1
   if (a is greater than b by the ordering criterion)
      return 1
   // a must be equal to b
   return 0
}

To compare numbers instead of strings, the compare function can simply subtract b from a:

function compareNumbers(a, b) {
   return a - b
}

JavaScript uses a stable sort: the index partial order of a and b does not change if a and b are equal. If a's index was less than b's before sorting, it will be after sorting, no matter how a and b move due to sorting.

The behavior of the sort method changed between JavaScript 1.1 and JavaScript 1.2. In JavaScript 1.1, on some platforms, the sort method does not work. This method works on all platforms for JavaScript 1.2.

In JavaScript 1.2, this method no longer converts undefined elements to null; instead it sorts them to the high end of the array. For example, assume you have this script:

<SCRIPT>
a = new Array();
a[0] = "Ant";
a[5] = "Zebra";

function writeArray(x) {
   for (i = 0; i < x.length; i++) {
      document.write(x[i]);
      if (i < x.length-1) document.write(", ");
   }
}

writeArray(a);
a.sort();
document.write("<BR><BR>");
writeArray(a);
</SCRIPT>

In JavaScript 1.1, JavaScript prints:

ant, null, null, null, null, zebra 
ant, null, null, null, null, zebra

In JavaScript 1.2, JavaScript prints:

ant, undefined, undefined, undefined, undefined, zebra 
ant, zebra, undefined, undefined, undefined, undefined

Examples

The following example creates four arrays and displays the original array, then the sorted arrays. The numeric arrays are sorted without, then with, a compare function.

<SCRIPT>
stringArray = new Array("Blue","Humpback","Beluga")
numericStringArray = new Array("80","9","700")
numberArray = new Array(40,1,5,200)
mixedNumericArray = new Array("80","9","700",40,1,5,200)

function compareNumbers(a, b) {
   return a - b
}

document.write("<B>stringArray:</B> " + stringArray.join() +"<BR>")
document.write("<B>Sorted:</B> " + stringArray.sort() +"<P>")

document.write("<B>numberArray:</B> " + numberArray.join() +"<BR>")
document.write("<B>Sorted without a compare function:</B> " + numberArray.sort() +"<BR>")
document.write("<B>Sorted with compareNumbers:</B> " + numberArray.sort(compareNumbers) +"<P>")

document.write("<B>numericStringArray:</B> " + numericStringArray.join() +"<BR>")
document.write("<B>Sorted without a compare function:</B> " + numericStringArray.sort() +"<BR>")
document.write("<B>Sorted with compareNumbers:</B> " + numericStringArray.sort(compareNumbers) +"<P>")

document.write("<B>mixedNumericArray:</B> " + mixedNumericArray.join() +"<BR>")
document.write("<B>Sorted without a compare function:</B> " + mixedNumericArray.sort() +"<BR>")
document.write("<B>Sorted with compareNumbers:</B> " + mixedNumericArray.sort(compareNumbers) +"<BR>")
</SCRIPT>

This example produces the following output. As the output shows, when a compare function is used, numbers sort correctly whether they are numbers or numeric strings.

stringArray: Blue,Humpback,Beluga
Sorted: Beluga,Blue,Humpback

numberArray: 40,1,5,200
Sorted without a compare function: 1,200,40,5
Sorted with compareNumbers: 1,5,40,200

numericStringArray: 80,9,700
Sorted without a compare function: 700,80,9
Sorted with compareNumbers: 9,80,700

mixedNumericArray: 80,9,700,40,1,5,200
Sorted without a compare function: 1,200,40,5,700,80,9
Sorted with compareNumbers: 1,5,9,40,80,200,700

splice

Changes the content of an array, adding new elements while removing old elements.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

splice(index, howMany, [element1][, ..., elementN])

Parameters

index	Index at which to start changing the array.
howMany	An integer indicating the number of old array elements to remove. If `howMany` is 0, no elements are removed. In this case, you should specify at least one new element.
element1, ..., elementN	The elements to add to the array. If you don't specify any elements, splice simply removes elements from the array.

Description

If you specify a different number of elements to insert than the number you're removing, the array will have a different length at the end of the call.

The splice method returns the element removed, if only one element is removed (howMany parameter is 1); otherwise, splice returns an array containing the removed elements.

Examples

The following script illustrate the use of splice:

<SCRIPT LANGUAGE="JavaScript1.2">

myFish = ["angel", "clown", "mandarin", "surgeon"];
document.writeln("myFish: " + myFish + "<BR>");

removed = myFish.splice(2, 0, "drum");
document.writeln("After adding 1: " + myFish);
document.writeln("removed is: " + removed + "<BR>");

removed = myFish.splice(3, 1)
document.writeln("After removing 1: " + myFish);
document.writeln("removed is: " + removed + "<BR>");

removed = myFish.splice(2, 1, "trumpet")
document.writeln("After replacing 1: " + myFish);
document.writeln("removed is: " + removed + "<BR>");

removed = myFish.splice(0, 2, "parrot", "anemone", "blue")
document.writeln("After replacing 2: " + myFish);
document.writeln("removed is: " + removed);

</SCRIPT>

This script displays:

myFish: ["angel", "clown", "mandarin", "surgeon"]

After adding 1: ["angel", "clown", "drum", "mandarin", "surgeon"]
removed is: undefined

After removing 1: ["angel", "clown", "drum", "surgeon"]
removed is: mandarin

After replacing 1: ["angel", "clown", "trumpet", "surgeon"]
removed is: drum

After replacing 2: ["parrot", "anemone", "blue", "trumpet", "surgeon"]
removed is: ["angel", "clown"]

The Array object overrides the toString method of Object. For Array objects, the toString method joins the array and returns one string containing each array element separated by commas. For example, the following code creates an array and uses toString to convert the array to a string.

var monthNames = new Array("Jan","Feb","Mar","Apr")
myVar=monthNames.toString() // assigns "Jan,Feb,Mar,Apr" to myVar

JavaScript calls the toString method automatically when an array is to be represented as a text value or when an array is referred to in a string concatenation.

In JavaScript 1.2 when you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag, toString returns a string representing the source code of the array.

<SCRIPT LANGUAGE="JavaScript1.2">
var monthNames = new Array("Jan","Feb","Mar","Apr")
myVar=monthNames.toString() // assigns '["Jan", "Feb", "Mar", "Apr"]'
                            // to myVar
</SCRIPT>

unshift

Adds one or more elements to the beginning of an array and returns the new length of the array.

Method of	`Array`
Implemented in	JavaScript 1.2, NES 3.0

Syntax

arrayName.unshift(element1,..., elementN)

Parameters

element1,...,
elementN

The elements to add to the front of the array.

Example

The following code displays the myFish array before and after adding elements to it.

myFish = ["angel", "clown"];
document.writeln("myFish before: " + myFish);
unshifted = myFish.unshift("drum", "lion");
document.writeln("myFish after: " + myFish);
document.writeln("New length: " + unshifted);

This example displays the following:

myFish before: ["angel", "clown"]
myFish after: ["drum", "lion", "angel", "clown"]
New length: 4

valueOf

Returns the primitive value of an array.

Method of	`Array`
Implemented in	JavaScript 1.1
ECMA version	ECMA-262

Syntax

valueOf()

Parameters

None

Description

The Array object inherits the valueOf method of Object. The valueOf method of Array returns the primitive value of an array or the primitive value of its elements as follows:

Object type of element Data type of returned value
Boolean
Boolean

Number or Date
number

All others
string

Object type of element	Data type of returned value
Boolean	Boolean
Number or Date	number
All others	string

This method is usually called internally by JavaScript and not explicitly in code.