HTML and CSS Reference
In-Depth Information
statements, and statements that create what are called programmer-defined functions. A function is one
or more statements that work together in a block and can be called anytime you need that functionality.
Functions save writing out the same code over and over. JavaScript supplies many built-in functions.
Certain functions are associated with objects (more on this later) and are called methods. The code
document.write("hello");
is a JavaScript statement that invokes the
write
method of the document object with the argument
"hello"
. An argument is additional information passed to a function or method. Statements are
terminated by semicolons. This piece of code will write out the literal string of characters h, e, l, l, o as part
of the HTML document.
The
document.write
method writes out anything within the parentheses. Since I wanted the information
written out to change as the date and time change, I needed a way to access the current date and time, so
I used the built-in JavaScript
Date
function. This function produces an object with the date and time.
Later, youll see how to use Date objects to compute how long it takes for a player to complete a game. For
now, all I want to do is display the current date and time information, and thats just what the code
document.write(Date());
does. To use the formal language of programming: this code calls (invokes) the
write
method of the
document
object, a built-in piece of code. The period (
.
) indicates that the
write
to be invoked is a
method associated with the document produced by the HTML file. So, something is written out as part of
the HTML document. What is written out? Whatever is between the opening parenthesis and the closing
parenthesis. And what is that? It is the result of the call to the built-in function
Date
. The
Date
function
gets information maintained by the local computer and hands it off to the
write
method.
Date
also
requires the use of parentheses, which is why you see so many. The
write
method displays the date and
time information as part of the HTML document, as shown in Figure 1-2. The way these constructs are
combined is typical of programming languages. The statement ends with a semi-colon. Why not a period?
A period has other uses in JavaScript, such as indicating methods and also for decimal points for
numbers.
Natural languages, such as English, and programming languages have much in common: different types
of statements; punctuation using certain symbols; and a grammar for the correct positioning of elements.
In programming, we use the term notation instead of punctuation, and syntax instead of grammar. Both
programming languages and natural languages also let you build up quite complex statements out of
separate parts. However, there is a fundamental difference: As I tell my students, chances are good that
much of what I say in class is not grammatically correct, but theyll still understand me. But when youre
“talking” to a computer via a programming language, your code must be perfect in terms of the grammatical
rules of the language to get what you want. The good news is that unlike a human audience, computers do
not exhibit impatience or any other human emotion so you can take the time you need to get things right.
Theres also some bad news that may take you a while to appreciate: If you make a mistake in grammar—
termed a syntactic error—in HTML, CSS, or JavaScript, the browser still tries to display something. Its up
to you figure out what and where the problem is when you don't get the results you wanted in your work.
Building the application and making it your own
You build an HTML document using a text editor and you view/test/play the document using a browser.
Though you can use any text editor program to write the HTML, I suggest TextPad for PCs and
TextWrangler for Macs. These are shareware, which makes them relatively inexpensive. Dont use a word
