Array Object

 Array Object

 

An array is a programming construct fundamental to nearly all languages today. Javascript is no different , providing the capability to construct and work with arrays. An array is simply a container holding a set of data elements. Each of the elements in an array is a separate value, but they exist as part of the array and cannot be accessed except by going through the array.

 

To define or access a particular element, you need to add brackets and an index value to the array variable. For example, you can define an array celled coffee as follows:

 

Coffee[0]= “Ethiopian sidamo”

Coffee[1]= ”kenyan”

Coffee[2]= “café Verona”

Coffee[3]= “Sumatra”

Coffee[4]= “costa rice”

Coffee[5]= “Columbian”

Coffee[6]= “bristan”

 

If you wanted to use any of these elements within a script, you could access them using the array variable along with an index value representing the location of the element within the array. Therefore , if you wanted to write the following line:

My favorite coffee is Ethiopian Sidamo

 

You would code the following:

Document.write(“My favorite coffee is”+coffee[0])

 

If array are new to you , you might find it helpful to think of an array as Javascript’s equivalent of a numbered list. It is really no more complicated than that. For example, suppose you have a list of ten items:

 

] Javascript

] Java

] Delphi

] C++

] Visual Basic

] Oracle Power Objects

] SmallTalk

] PowerBuilder

] Paradox

] Access

 

If you wanted to assemble this group of items in a javascript array, it would look like the following:

 

devTools[0]=”Javascript”

devTools[1]=”Java”

devTools[2]=”Delphi”

devTools[3]=”C++”

devTools[4]=”Visual Basic”

devTools[5]=”Oracle power objects”

devTools[6]=”SmallTalk”

devTools[7]=”PowerBuilder”

devTools[8]=”Paradox”

devTools[9]=”Access”

 

Creating an Array Object

 

Unlike a string, an array is not recognized as a data type in Javascript , but you can work with them as objects. The way in which you create Array objects varies depending on the browser you are doing.

 

Array Objects with Netscape Navigator 3.0

 

Netscape Navigator 3.0 enables you to work with arrays as true Javascript objects. You can create instances of an Array object using the new operator. For example, if you wanted to create the coffee array defined earlier, you would define it as follows:

 

var coffee=new Array()

Coffee[0]= “Ethiopian sidamo”

Coffee[1]= ”kenyan”

Coffee[2]= “café Verona”

Coffee[3]= “Sumatra”

Coffee[4]= “costa rice”

Coffee[5]= “Columbian”

Coffee[6]= “bristan”

 

The new operator an array object, and the statements following fill the array with data elements.

 

An alternative way to define an array object is to specify the data elements as parameters of the new call. For example, the following line is the functional equivalent of the previous example:

 

Var coffee=new Array(7)

 

Notice that you did not specify a size of the array , as is common place in many programming languages. Javascript does not require that you specify the size of the array, which allows you to incrementally expand the array as you add each new data element. However, if you want to, you can specify the size of the array initially as a parameter in the new expression. Alternatively , you could also resize an array simply by defining a data element at the n position. If n is the highest number defined in the array, then the new array size is expanded to n+1.

Example

 

Var javaDrinks=new Array()

javaDrinks[0]=”Regular Coffee”

javaDrinks[1]=”Decaf Coffee”

javaDrinks[2]=”café Mocha”

javaDrinks[3]=”café Lait”

javaDrinks[4]=”café latte”

 

The size of the javaDrinks array is 200, even though only five data elements are defined. Each undefined elements returns a null value if you access it.

 

You can retrieve the size of the array using the Array object’s length property. For example , if you wanted to iterate through each element in an array object, you could use the script shown in listing

<script language=”Javascript”>

Var coffee=new Array();

document.write(“coffees of the world:<p>”)

for(var i=0;i<coffee.length;i++)

{

document.write(i+1+”. ”+coffee[i]+”<p>”)

}

</script>