Chapter 10: JavaScript Functions

1
Chapter 10 JavaScript Functions

• CIS 275Web Application Development for Business I

2
Program Modules in JavaScript

• Software development is best achieved in smaller
  pieces called _________, applying the principle
  of divide and conquer.
• A module in JavaScript is called a _________.
• A pre-defined function that belongs to a class is
  called a method (like Math.pow or Math.round).
• A function you write is called a
  ____________-defined function.
• A function is invoked by a function call.
• A function call may include arguments.
• A called function may _______ data to the caller.

3
Programmer-Defined Functions

• All variables declared in a function are _______.
• A function declaration may include parameters,
  which are also local variables.
• Functions enable the principle of software reuse
  and help to avoid code repetition.
• Format of a function definition
• function function-name ( parameter-list )
• declarations and statements
• The ___ is the function call operator.
• The first line is the function declaration and
  the content within the s is the function
  ______.

()
4
Fig. 10.2

• lthtml xmlns "http//www.w3.org/1999/xhtml"gt
• ltheadgt
• lttitlegtA Programmer-Defined
  Functionlt/titlegt
• ltscript type "text/javascript"gt
• document.writeln(
• "lth1gtSquare numbers from 1 to
  10lt/h1gt" )
• for ( var x 1 x lt 10 x )
• document.writeln( "The square of "
  x
• " is " square( x ) "ltbr /gt" )
• function square( y ) // do NOT use var
  here
• return y y
• lt/scriptgt
• lt/headgt
• ltbodygtlt/bodygt
• lt/htmlgt

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Example of a Function Call

• lthtmlgt
• ltheadgt
• ltscript type"text/javascript"gt
• function myFunction()
• alert("HELLO")
• lt/scriptgt
• lt/headgt
• ltbodygt
• ltformgt
• ltinput type "button" onclick "myFunction()"
• value "Call function" gt
• lt/formgt
• ltpgtBy pressing the button, a function will be
  called. The function will alert a message.lt/pgt
• lt/bodygt
• lt/htmlgt

6
Function Call w/ Arguments and Return

• lt?xml version "1.0"?gt
• lt!DOCTYPE html
• PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
• "http//www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd
  "gt
• lthtmlgt
• ltheadgt
• ltscript type"text/javascript"gt
• function total(numberA, numberB)
• return numberA numberB
• lt/scriptgt
• lt/headgt
• ltbodygt
• ltscript type"text/javascript"gt
• document.write( total(2,3) )
• lt/scriptgt
• lt/bodygt
• lt/htmlgt

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10.8 Scope Rules

• The scope of an identifier for a variable or
  function is the part of the program in which the
  identifier can be referenced.
• Variables declared in the ______ element are
  global variables and have global scope.
• Variables declared inside a function have ______
  scope and can be used only in that function.
• Function parameters also have local scope.
• A variable with local scope will ______ a
  variable with the same name that has global scope.