Document Object
JavaScript provides a number of application objects such as the document,
window, string, and Date objects. Each object has properties that can be read
and sometimes set in JavaScript statements. Many objects have methods such as
document.write() that give the object
significant functionality. Information about the object often called the
attributes of the object are stored in variables called "properties"
of the object. Some of the basic properties and methods of the document object
are introduced below using simple JavaScript statements.Properties
Properties are the attributes of an object. For example the background color and the URL the document was retrieved from are attributes of an HTML
document. In the examples below various properties of the document object are
accessed using the dot operator and assigned to a variable called
result.Getting the Properties of an Object
result = document.location
result will contain the
URL of the document.result = document.lastModified
result will contain the
date of the last time the document was modified.result = document.bgColor
result will contain the
background colour of the document.Setting the Properties of an Object
It is also possible to assign values to some object properties. So while it
does not make sense to be able to change the location where the document came
from, you can change the background color of the document this way:
document.bgColor = "#800080"
Methods
Methods are a way of asking an object to do something more complicated than
changing a property. For example:
document.write( JavaScript expression )
write() is a method (a
function) that belongs to the document object. Calling write() is like asking a document to
append HTML to itself. The JavaScript expression inside the round brackets will
be evaluated and the result (whatever it is) written out to the HTML page. Here
are some more methods for the document object:document.writeln( JavaScript expression )
writeln() does the same
thing as the write() method
except that it appends a new line character to the string of text it writes
into the document. writeln is a convenient method to use when writing out data
from short test programs within <PRE></PRE>
tags. Here are some more methods for the document object:document.clear()
Clears the document (doesn't appear to do anything in Netscape 2.02)
document.close()
"Closes the output stream and forces data sent to layout to
display." In Netscape 2.02 it is not required to display the last output.
document.open()
"Opens a stream to collect the output of write or writeln
methods."
