Lesson 7: FUNCTIONS
There
are two parts of a function: The definition and the call.
Defining
the function simply names the function and specifies what to
do when the function is called. Functions should be defined in the <head></head>
of the HTML document.
Calling
the function actually performs
the specified actions which are usually defined in the <Head>.
In this lesson the function is called when the button is clicked on.
Functions
are only stored, and are not executed until certain actions are performed
by the user of the web page. Defining a function in the Head guarantees
that functions are loaded before the user has a chance to do anything
that might call a function. This is important because if an undefined
function is called, this will lead to an error. It is also a good idea
to define functions in the <head> because it makes your code modular
so you can use the same function as an event
handler for many different items. This also makes your code easier
to read.
Variables
and Functions
When
you declare a variable within a function, the variable can only be accessed
within that function. When you exit the function, the variable is destroyed.
These variables are called local variables. You can have local variables
with the same name in different functions, because each is recognized
only by the function in which it is declared.
If you
declare a variable outside a function, all the functions on your page
can access it. The lifetime of these variables starts when they are
declared, and ends when the page is closed.
