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You can think of an array as a set of boxes containing
information. So we can say: MyNumbers=new Array
("1","2","3","4","5","6","7","8","9","0",".");
On this page:
- Defining the Array
- Length of the Array
- Find Element at Position
- Different Ways of Making an Array
In the HEAD of the document I define my array:
<script type= "text/javascript">
<!---
MyNumbers= new Array
( "1","2","3","4","5","6","7","8","9","0",".");
//-->
</script>
With this array we can do some things.
When I click this button, it tells me that the length of my array is 11. (Which seems
correct!). It says, more precisely that:
MyNumbers.length=11
Here I have put some code into the button (bad style!):
onclick="alert
('The length of my array, MyNumbers.length is '+ MyNumbers.length)"
 Be aware that the above code could be wrapped in your
browser giving an 'unterminated string' error on copying. The break between the alert and
the rest is not important. It is the broken string that is important!
That is we can get the length of an Array by using the above code.
We can also find the item in an array at a given position. Using the array:
MyWords=new Array("ant","boar","cat","dog",
"elephant","fish","goat","hover bird!!!",
"insect","jabberwocky","kernel")
Put a number in the box below and press the button to get the element at that position:
If I enter a number from 0 to 10 I get a message telling me the item at that
position in the array. If I enter another character, then I get the answer 'undefined'.
The elements in an array are defined for the positions 0 to 10, but outside these numbers
there are no elements defined. The elements in an array are identified by their position
number, beginning at 0, and, in this case, ending at 10.
The code in this button is:
onclick="alert('The element in position '
+this.form.T1.value+
' is the
element \''+
MyWords[this.form.T1.value]+'\'');
return false"
 The keyword, this,
refers to the element that contains it. (My form, etc) It can have a meaning like 'my'. So
in this case, the message from the button. this.form
defines the button's form in the document, and we do not need to name the form! T1 is the name of the text box.
If we put 3 in the text box, JavaScript will compute the value of:
MyWords[3]
which is the 4th element (starting from 0), or the word, 'dog'.
Here are three ways of defining an array:
The first is an old way of declaring an array:
myArray=[ "ant","bat","cat"]
alert( "Literal array element
zero is "+myArray[0]);
Here we define an array step-by-step:
myArray= new Array(3)
myArray[0]= "ant";
myArray[1]= "bat"
myArray[2]= "cat"
alert( "The third element is
"+myArray[2])
And here we define the array more
economically:
//Dense array
myArray= new Array("ant","bat","cat")
alert( "Dense array element one
is "+myArray[1]);
Why not copy the above code and try it in the browser?
We can do lots of fun things with arrays, but before we do, let's make sure we
understand about select boxes in forms ...
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JavaScript
Tutorial 1 Java Script Tutorial TOC
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