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Core JavaScript Reference 1.5:

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Core JavaScript Reference 1.5





Array

Lets you work with arrays.


Core object

Implemented in  

JavaScript 1.1, NES 2.0

JavaScript 1.3: added toSource method; changed length property; changed push method  

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)

JavaScript 1.2 when you do not specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag:

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

JavaScript 1.1:

new Array([arrayLength])
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.

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"

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
 


Backward Compatibility

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

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

 

Reflects 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 new length of 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.  

toSource

 

Returns an array literal representing the specified array; you can use this value to create a new array. Overrides the Object.toSource method.  

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  

ECMA version  

ECMA-262  


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


Parameters



arrayName2...
arrayNameN

 

Arrays to concatenate to this array.  


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:

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]


constructor

Specifies the function that creates an object's prototype. Note that the value of this property is a reference to the function itself, not a string containing the function's name.



Property of  

Array  

Implemented in  

JavaScript 1.1, NES 2.0  

ECMA version  

ECMA-262  


Description
See Object.constructor.


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


See also
Array.reverse


length

An unsigned, 32-bit integer that specifies the number of elements in an array.



Property of  

Array  

Implemented in  

JavaScript 1.1, NES 2.0

JavaScript 1.3: length is an unsigned, 32-bit integer with a value less than 232.  

ECMA version  

ECMA-262  


Description
The value of the length property is an integer with a positive sign and a value less than 2 to the 32 power (232).

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  

ECMA version  

ECMA-262 Edition 3  


Syntax
pop()


Parameters
None.


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

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


See also
push, shift, unshift


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 new length of the array. This method changes the length of the array.



Method of  

Array  

Implemented in  

JavaScript 1.2, NES 3.0

JavaScript 1.3: push returns the new length of the array rather than the last element added to the array.  

ECMA version  

ECMA-262 Edition 3  


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.


Backward Compatibility

JavaScript 1.2. The push method returns the last element added to an array.


Example
The following code creates the myFish array containing two elements, then adds two elements to it. After the code executes, pushed contains 4. (In JavaScript 1.2, pushed contains "lion" after the code executes.)

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


See also
pop, shift, unshift


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()


Parameters
None


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:


See also
Array.join, Array.sort


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  

ECMA version  

ECMA-262 Edition 3  


Syntax
shift()


Parameters
None.


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


See also
pop, push, unshift


slice

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



Method of  

Array  

Implemented in  

JavaScript 1.2, NES 3.0  

ECMA version  

ECMA-262 Edition 3  


Syntax
slice(begin[,end])


Parameters



begin

 

Zero-based index at which to begin extraction.  

end

 

Zero-based index at which to end extraction:

 


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:

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:

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


See also
Array.join, Array.reverse


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

JavaScript 1.3: returns an array containing the removed elements.  

ECMA version  

ECMA-262 Edition 3  


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 an array containing the removed elements. If only one element is removed, an array of one element is returned.


Backward Compatibility

JavaScript 1.2. The splice method returns the element removed, if only one element is removed (howMany parameter is 1); otherwise, the method 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"]


toSource

Returns a string representing the source code of the array.



Method of  

Array  

Implemented in  

JavaScript 1.3  


Syntax
toSource()


Parameters
None


Description
The toSource method returns the following values:

This method is usually called internally by JavaScript and not explicitly in code. You can call toSource while debugging to examine the contents of an array.


Examples
To examine the source code of an array:

alpha = new Array("a", "b", "c")
alpha.toSource() //returns ["a", "b", "c"]


See also
Array.toString


toString

Returns a string representing the specified array and its elements.



Method of  

Array  

Implemented in  

JavaScript 1.1, NES 2.0  

ECMA version  

ECMA-262  


Syntax
toString()


Parameters
None.


Description
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.


Backward Compatibility

JavaScript 1.2. When you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag, toString returns a string representing the source code of the array. This value is the same as the value returned by the toSource method in JavaScript 1.3 and later versions.

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


See also
Array.toSource


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  

ECMA version  

ECMA-262 Edition 3  


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


See also
pop, push, shift


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  

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


See also
Object.valueOf


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Last Updated September 28, 2000