3/18/2009
1
Simplifying buttons
consider the button from greetbox.html:
the size of the onclick attribute makes the button complex
and difficult to read
plus, must be careful with nested quotes ("…" vs. '…')
Simplifying buttons
functions provide a mechanism for simplifying complex
buttons such as this
recall from Chapter 5:
we used predefined JavaScript functions to accomplish
some of the work that needed to be done
Math.random
Math.floor
functions reduce the length and complexity of code
e.g., a single call to Math.sqrt replaces the underlying
complex algorithm
Simple user-defined functions
in addition to JavaScript's predefined functions, the user
can define new functions in the HEAD section and call
them within the page
Simple user-defined functions
a function definition begins with the word function
followed by its name and ()
a function name should be descriptive of the task being
performed
lines beginning with // are comments that describe the
function's behavior
comments are ignored by the interpreter, but make code
more user-readable
the statements to be executed when the function is
called are placed between the curly braces
the code from the
button is moved to the
user-defined Greet
function
as a result, the button
is greatly simplified
GENERAL RULE: if
more than one
statement is to be
associated with a
button, define a
separate function
Chapter 9
Abstraction and User-Defined Functions
