Transcript Tutorial 10

XP
Tutorial 10
Working with JavaScript
Creating a Programmable Web Page for North Pole
Novelties
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
1
XP
Objectives
• Introducing JavaScript
• Inserting JavaScript into a Web Page File
• Writing Output to the Web Page
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
2
XP
Objectives
•
•
•
•
•
Working with Variables and Data
Working with Dates
Working with Expressions and Operators
Creating JavaScript Functions
Creating the XmasDays Function
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
3
XP
Objectives
•
•
•
•
Working with Conditional Statements
Using Arrays
Working with Program Loops
Debugging Your JavaScript Programs
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
4
XP
Introduction to JavaScript
• Server-side Programs pose problems
• Client-side Programs were developed to
run programs and scripts on the client side
of a Web browser.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
5
XP
The Development of JavaScript
• JavaScript is a subset of Java.
• Differences between Java and JavaScript:
– Java is a compiled language
– JavaScript is an interpreted language
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
6
XP
Comparing Java and JavaScript
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
7
XP
The Development of JavaScript
• Jscript is a version of JavaScript supported
by Internet Explorer.
• The European Computer Manufacturers
Association (ECMA) develops scripting
standards.
– The standard is called ECMAScript but browsers
still generally call is JavaScript.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
8
Inserting JavaScript into a WebXP
Page File
• Outline the main tasks you want the program
to perform first.
• A JavaScript program can either be placed
directly in a Web page file or saved in an
external text file.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
9
Inserting JavaScript into a WebXP
Page File
• Insert a client-side script in a Web page when
using the script element.
• Comments are useful for hiding scripts from
older browsers.
• Specify alternative content using the
nonscript element for browsers that don’t
support scripts (or have their script support
disabled).
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
10
XP
Writing Output to the Web Page
• An object-oriented programming language
writes the output by manipulating tasks.
• An action you perform on an object is called a
method.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
11
XP
Working with Variables and Data
• A variable is a named item in a program that
stores information.
• Variable names have restrictions (see pages
HTML 531-532).
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
12
XP
Working with Variables and Data
• JavaScript variable types:
–
–
–
–
Numeric variables
String variables
Boolean variables
Null variables
• You must declare a variable before using it.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
13
XP
Working with Variables and Data
• Numeric variable- any number, such as 13, 22.5,
etc.
– Can also be expressed in scientific notation.
• String variable- any group of text characters, such
as “Hello” or “Happy Holidays!”
– Must be enclosed within either double or single quotations
(but not both).
• Boolean variable- accepts only true and false values
• Null variable- has no value at all.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
14
XP
Working with Dates
• Create a date object to store date information.
Date Methods
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
15
Working with Expressions andXP
Operators
• Expressions are JavaScript commands that assign
values and variables.
• Operators are elements that perform actions within
expressions.
– Arithmetic operators: perform simple mathematical
calculations
– Binary operators: work on two elements in an expression
– Unary operators: work on only one variable
– Increment operators: can be used to increase the value of a
variable by 1
– Assignment operators: used to assign values in expressions
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
16
Working with Expressions andXP
Operators
• The Math object is a JavaScript object used for
calculations other than simple math.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
17
XP
Creating JavaScript Functions
• A function is a series of commands that
perform an action or calculates a value.
• A function name identifies a function.
• Parameters are values used by the function.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
18
XP
Working with Conditional
Statements
• Conditional statements are commands that
run only when specific conditions are met.
• Conditional statements require a Boolean
expression.
– you need one of the following operators to create
a Boolean expression:
• Comparison operator
• Logical operator
• Conditional operator
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
19
XP
Using Arrays
• An array is an ordered collection of values
referenced by a single variable name.
var variable = new Array (size);
Where variable is the name of the array variable and
size is the number of elements in the array.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
20
XP
Working with Program Loops
• A program loop is a set of instructions that is
executed repeatedly.
– Use program loops to configure a group of
commands to be executed a set number of times.
– The loop uses a counter to track the number of
times the command block has been run.
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
21
XP
Working with Program Loops
Creating a For loop
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
22
XP
Working with Program Loops
Nesting a For loop
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
23
XP
Working with Program Loops
Creating a While loop
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
24
XP
Working with Program Loops
Nesting a While loop
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
25
XP
Debugging Your JavaScript
Programs
• Three types of errors:
– Load-time errors (occurs when the script is
loading)
– Run-time errors (occurs when the being executed)
– Logical errors (free from syntax and structural
mistakes, but result in incorrect results)
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
26
XP
Common Mistakes
• You need to debug your program to fix the
mistakes.
• Common mistakes include:
–
–
–
–
–
–
Misspelling a variable name
Mismatched parentheses or braces
Mismatched quotes
Missing quotes
Using ( instead of [
Using = in place of ==
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
27
XP
Debugging Tools and Techniques
• To avoid making mistakes and quickly located
those you do make:
– Write modular code
– Use the Microsoft Script Debugger to debug (for
use with Internet Explorer)
– Use the Netscape JavaScript Console to debug
(for use with Netscape)
Tutorial 10
New Perspectives on HTML and XHTML,
Comprehensive
28