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An array is a programmer's term for something which can hold many
objects of the same type. In the example given here the array holds
the links (JavaScript's way of getting at <A ...> tags) which
have been entered in this document.
One way to visualise an array in JavaScript is as a set of boxes,
each with a number. The numbering starts at zero, the last box is
numbered as the total number of boxes minus 1. Hence if this document
has 2 links, there would be two boxes in the links array object.
The length property of the array object is therefore two.
- To access the first entry (or box) we supply the index of zero.
- To get the second we use the number one (programmers were never
great mathematicians, which is why they start counting at zero,
end of digression).
- To get at the last entry we use the notation length - 1, which
in this example gives one.
- The notation used to get at a particular entry is using the
[ and ] to enclose the index we are interested in.
For example:
To access the first link object of this document we use the notation:
document.links[0]
To get at the array's only property (length), we write:
document.links.length
To get at the href property of the last link in the array,we
could write the following:
document.links[document.links.length - 1].href
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From what I can gather a JavaScript array has only one property,
length, which says how many entries the array has. Consider the
links array member of the document
object. Here are some of its current contents:
The code to produce the above is as follows:
In the <HEAD> ... </HEAD> part a JavaScript function
was defined/declared:
<SCRIPT LANGUAGE="JavaScript">
function DoPrintLinks()
{
var nCount = 0
var nEnd = document.links.length
document.writeln("According to JavaScript, this document
has ",
nEnd, " link(s) in it.", "<UL>")
for (nCount = 0 ; nCount < nEnd ; nCount ++)
{
document.writeln("< LI >", document.links[nCount].href,"<
/LI >")
}
document.writeln("< /UL >")
}
</script>
Explanation:
At the appropriate place in the document's body, a call to the
function is placed as follows:
Expalantion:
- The function is called upon to print each link.
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Note: Only the links which appear before the call to the function
are printed. This is because JavaScript works its way through the
document in a linear fashion. When the call to the function is encountered,
JavaScript has not read the rest of the document yet.
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