XP Tutorial 10New Perspectives on HTML and XHTML, Comprehensive 1 Working with JavaScript Creating a...

Tutorial 10 New Perspectives on HTML and XHTML, Comprehensive

Working with JavaScript

Creating a Programmable Web Page for North Pole Novelties

Tutorial 10

XPObjectives

• Introducing JavaScript• Inserting JavaScript into a Web Page File• Writing Output to the Web Page

XPObjectives

• Working with Variables and Data• Working with Dates• Working with Expressions and Operators• Creating JavaScript Functions• Creating the XmasDays Function

XPObjectives

• Working with Conditional Statements• Using Arrays• Working with Program Loops• Debugging Your JavaScript Programs

XPIntroduction 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.

XPThe Development of JavaScript

• JavaScript is a subset of Java.• Differences between Java and JavaScript:

– Java is a compiled language– JavaScript is an interpreted language

XPComparing Java and JavaScript

XPThe 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.

XPInserting JavaScript into a Web 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.

XPInserting JavaScript into a Web 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).

XPWriting 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.

XPWorking 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).

• JavaScript variable types:– Numeric variables– String variables– Boolean variables– Null variables

• You must declare a variable before using it.

• 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.

XPWorking with Dates

• Create a date object to store date information.

Date Methods

XPWorking with Expressions and 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

XPWorking with Expressions and Operators

• The Math object is a JavaScript object used for calculations other than simple math.

XPCreating 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.

XPWorking 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

XPUsing 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.

XPWorking 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.

Creating a For loop

Nesting a For loop

Creating a While loop

Nesting a While loop

XPDebugging 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)

XPCommon 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 ==

XPDebugging 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)

XP Tutorial 10New Perspectives on HTML and XHTML, Comprehensive 1 Working with JavaScript Creating a...

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