JavaScript Guide

This JavaScript Guide was last modified

JavaScript Basics
What We Can Do with JavaScript
Embedding JavaScript in HTML
Using the JavaScript Console
Using JavaScript Objects
Window Methods
Handling Events
Using the Status Bar
Validating Form Input
Using Windows and Frames
Creating a Frame
Using JavaScript URLs


What is JavaScript?

JavaScript is a cross-platform, object-based scripting language

Netscape provides on-line JavaScript documentation

Client-side JavaScript is embedded directly in HTML pages and is interpreted by browser at runtime

Client-side JavaScript statements embedded in HTML page can respond to user events such as mouse-clicks, form input, and page navigation

Microsoft Internet Explorer also supports JavaScript, but has some additional features and calls its version "JScript"

JavaScript syntax much like Java, C, C++

JavaScript language resembles Java but does not have Java's static typing and strong type checking. That means you do not have to declare what type a variable is in JavaScript like you have to in Java.

JavaScript and Java have nearly same expression syntax and basic control-flow constructs

JavaScript -- Interpreted (not compiled) by client
Java -- Compiled bytecodes downloaded from server, executed on client

JavaScript -- Code integrated with, and embedded in, HTML
Java -- Applets distinct from HTML (but accessed from HTML pages)

JavaScript Basics

Values -- numbers (42, 3.14159), logical values (true, false), strings ("Purdue University")

Use variables as symbolic names for values. Must start with letter or underscore (_). Subsequent characters can also be digits (0-9).

Declare a variable via
var x;

Character string is zero, one, or more characters enclosed in double (") or single (') quotation marks

Expression is any valid set of values, variables, operators, and expressions that evaluates to single value; value can be number, string, or logical value

Basic assignment operator is equal (=)

Standard arithmetic operators are addition (+), subtraction (-), multiplication (*), and division (/)

Comparison operators are equal (==), not equal (!=), greater than (>), greater than or equal (>=), less than (<), less than or equal (<=)

JavaScript is object-based

Object has properties (fields)

Object has functions associated with it that are known as the object's methods

Function is JavaScript procedure -- set of statements that performs specific task

if...else Statement

if (condition) { statements1 } else { statements2 } if (form1.threeChar.value.length == 3) { return true; } else { alert("Enter exactly three characters. " + document.form1.threeChar.value + " is not valid."); return false; } switch Statement

switch (expression) { case label : statement; break; case label : statement; break; ... default : statement; } switch (fruit) { case "Oranges" : document.write("Oranges are $0.59 a pound.<BR>"); break; case "Apples" : document.write("Apples are $0.32 a pound.<BR>"); break; case "Bananas" : document.write("Bananas are $0.48 a pound.<BR>"); break; case "Cherries" : document.write("Cherries are $3.00 a pound.<BR>"); break; default : document.write("Sorry, we are out of " + fruit + ".<BR>"); } for Statement

for (initial; condition; increment) { statements } for (i=0; i<selectObj.options.length; i=i+1) { if (selectObj.options[i].selected==true) { numberSelected = numberSelected +1; } } while Statement

while (condition) { statements } n = 0; x = 0; while( n < 3 ) { n = n+1; x = x+n; } do...while Statement

do { statement } while (condition); do { i=i+1; document.write(i); } while (i<5);

What We Can Do with JavaScript

(1) Build HTML dynamically

(2) Monitor user events and take actions -- such as...
clicking button or link
changing form field
moving mouse on or off link

Embedding JavaScript in HTML

SCRIPT tag is extension to HTML that can enclose JavaScript statements

<SCRIPT LANGUAGE="JavaScript"> JavaScript statements... </SCRIPT> Document can have multiple SCRIPT tags and, thus, multiple groups of JavaScript statements

Browser executes code within SCRIPT container.

Some browsers do NOT support JavaScript. To ensure that these browsers ignore the JavaScript code, place entire script within HTML comment tags, and precede ending comment tag with double-slash (//) that indicates JavaScript single-line comment.

<SCRIPT LANGUAGE="JavaScript"> <!-- Hide script from some browsers JavaScript statements... // end script hiding from some browsers --> </SCRIPT> Simple script...

<HTML> <HEAD> <TITLE>My first JavaScript!</TITLE> </HEAD> <BODY> <SCRIPT LANGUAGE="JavaScript"> <!-- Hide script from some browsers document.write ("My first JavaScript!"); // end script hiding from some browsers --> </SCRIPT> JavaScript can be used to create text that is displayed along with text appearing in the BODY of the file. </BODY> </HTML> Try it

SRC attribute of SCRIPT tag lets you specify file as JavaScript source (rather than embedding JavaScript in HTML)

JavaScript statements within SCRIPT tag with SRC attribute are ignored unless inclusion has error

<HEAD> <TITLE>My Page</TITLE> <SCRIPT SRC="common.js"> document.write ("Oops. Something went wrong in getting the JavaScript file!"); </SCRIPT> </HEAD>


Define functions for page in HEAD portion of document

JavaScript Calculator

JavaScript Adding Machine that does NOT work

JavaScript Adding Machine that DOES work

<HEAD> <SCRIPT LANGUAGE="JavaScript"> <!-- Hide script from some browsers function increase (number) { return (number + 1); } // end script hiding from some browsers --> </SCRIPT> </HEAD> <BODY> <SCRIPT LANGUAGE="JavaScript"> document.write("The function returned ", increase(7), "."); </SCRIPT> <P> That is all.... <P> </BODY> Try it

write method of document displays output on screen

<HEAD> <SCRIPT LANGUAGE="JavaScript"> <!--- Hide script from some browsers // This function displays a horizontal rule // of specified width function rule(width) { document.write("<HR ALIGN=LEFT WIDTH=" + width + "% NOSHADE>\n"); } // This function displays a heading // of specified level and some text function heading(headLevel, headText, text) { document.write("<H", headLevel, ">", headText, "</H", headLevel, ">\n", text, "<P>\n") } // end script hiding from some browsers --> </SCRIPT> </HEAD> <BODY> <H1>Using the write method</H1> <SCRIPT LANGUAGE="JavaScript"> <!--- hide script from some browsers rule(25); heading(2, "The write method", "Notice the use of + and ,"); // end script hiding from some browsers --> </SCRIPT> This is some standard HTML, unlike the above that is generated.<P> </BODY> Try it

Using the JavaScript Console

Suppose that you make an error in your JavaScript

Type "javascript:" into Location for details

But this will not catch all errors

Using JavaScript Objects

navigator: properties for name and version of browser being used

window: properties for entire window (also window object for each window in framed document)

document: properties for document content, such as title, background color, links, forms

To refer to specific properties, specify object name and all ancestors

Generally, object gets name from NAME attribute of corresponding HTML tag

document.sform.schoolname.value value property of schoolname text field in form named sform in current document

The JavaScript Date Object

Window Methods

alert: displays an alert box with message

confirm: displays confirm dialog box with OK and Cancel buttons

prompt: displays prompt dialog box with text field for entering a value

If you want to know about Prompts, well then <SCRIPT LANGUAGE="JavaScript"> document.write(prompt("Enter your name:", "Justin")); </SCRIPT> this page is for you! JavaScript prompt

<FORM METHOD=POST ENCTYPE="text/plain" onSubmit="return(confirm(kid.value + ': The information you gave is ' + 'being e-mailed to us. ' + 'We will get in touch with you in ' + '3-5 days.'))"> JavaScript confirmation

setTimeout: evaluates expression or calls function once after specified period elapses (in milliseconds -- thousandths of seconds)

setInterval: evaluates expression or calls function each time specified period elapses (in milliseconds)

location: redirects client to another URL as if user had clicked hyperlink

location = ""; Pick and Click with Javascript

document object properties: title, bgColor, fgColor, linkColor, alinkColor, vlinkColor, lastModified (date document was last modified), referrer (previous URL client visited), and URL (URL of document)

window object properties: innerHeight, innerWidth, outerHeight, outerWidth (inner and outer height and width of browser window -- can be changed to resize window)

navigator object properties: appName (name of browser ... Netscape), appVersion (version information ... 4.7)

document.topform document.fillform document.lastform Form objects stored in array called forms

document.forms[0] document.forms[1] document.forms[2] Elements in form (text fields, radio buttons, etc.) also stored in elements array

document.forms[1].elements[3] Also arrays for document.applets, document.images, document.links, window.frames

Using form arrays

document.writeln("Title --", document.title, "<BR>"); document.writeln("URL --", document.URL, "<BR>"); document.writeln("Background color --", document.bgColor, "<BR>"); document.writeln("Last Modified --", document.lastModified, "<BR>"); document.writeln("Referred by --", document.referrer, "<BR>"); document.writeln("Inner height of window --", window.innerHeight, "<BR>"); document.writeln("Inner width of window --", window.innerWidth, "<BR>"); document.writeln("Outer height of window --", window.outerHeight, "<BR>"); document.writeln("Outer width of window --", window.outerWidth, "<BR>"); document.writeln("Web browser is --", navigator.appName); document.writeln(" version ", navigator.appVersion, "<BR>"); Try it

window.innerWidth=450; window.innerHeight=250; Try it

Handling Events

Events are actions that occur usually as result of something user does --
clicking button or link
changing form field
moving mouse on or off link

Event handlers and events:

onFocus - user gives input focus to window or form element

onBlur - user removes input focus from window or form element

onChange - user changes text field, textarea, select list

onClick - user clicks button or link

onLoad - (used in <BODY> or <FRAMESET>) done when Web page loads initially

onMouseOver - user moves cursor over link

onMouseOut - user moves cursor out of client-side image map or link

onSubmit - user clicks SUBMIT button in form

<TAG eventHandler="JavaScript Code"> where TAG is HTML tag, eventHandler is name of the event handler, JavaScript Code is function call (usually) or JavaScript statements

<INPUT TYPE="button" VALUE="Calculate" onClick="compute(this.form)"> this refers to current object -- the button
this.form refers to form containing the button

<SCRIPT LANGUAGE="JavaScript"> <!-- Hide script from some browsers function compute(fm) { if (confirm("Is this what you want?")) fm.result.value = eval(fm.expr.value) else setInterval ('alert("Please try again!")',10000) } // end script hiding from some browsers --> </SCRIPT> </HEAD> <BODY> <FORM> Enter some expression: <INPUT TYPE="text" NAME="expr" SIZE=15> <INPUT TYPE="button" VALUE="Calculate" onClick="compute(this.form)"> <BR> Result: <INPUT TYPE="text" NAME="result" SIZE=15> </FORM> </BODY> Try it

JavaScript Message Scroller

JavaScript onMouseOver can be used along with HREF in a standard link or in a client side image map

JavaScript onMouseOver can be used to change the appearance of images

OnMouseOver can also be used for changing images and popping up alerts

The Elusive "Click Here" Image

"Real world" example of OnMouseOver and OnMouseOut

Animated Images Using JavaScript

Protecting Images Using JavaScript

An Evolving Background Color Using JavaScript

Using the Status Bar

Two window properties display messages in the browser status bar

defaultStatus appears when nothing else is in status bar

status displays transient message in status bar

<SCRIPT LANGUAGE="JavaScript"> <!-- Hide script from some browsers defaultStatus = "Watch this status line as you move the mouse over the image map"; // end script hiding from some browsers --> </SCRIPT> <AREA SHAPE="RECT" COORDS="26,72,145,146" HREF="" onMouseOver="window.status='Go to NBC'; return true" onMouseOut="window.status=''; return true"> Try it

Validating Form Input

JavaScript Handling of Forms

JavaScript Forms Example

Download each of the following JavaScript and mailto examples, change the "mailto" field, and try them out:
(1) Confirm information received via Browser window
(2) Confirm information received via JavaScript confirmation mini-window

As user enters it, onChange event handler on each form element that you want validated

When user submits form, onClick event handler on button that submits form

<SCRIPT LANGUAGE="JavaScript"> <!-- Hide script from some browsers function foc() { window.status="Please enter a number 1-999"; } function blu() { window.status=""; } function isaPosNum(s) { return (parseInt(s) > 0) } function qty_check(item, min, max) { var returnVal = false if (!isaPosNum(item.value)) alert("Please enter a positive number") else if (parseInt(item.value) < min) alert("Please enter a " + + " greater than " + min) else if (parseInt(item.value) > max) alert("Please enter a " + + " less than " + max) else returnVal = true return returnVal } function validateAndSubmit(theform) { if (qty_check(theform.quantity, 0, 999)) { alert("Order has been Submitted") return true } else { alert ("Sorry, Order Cannot Be Submitted!") return false } } // end script hiding from some browsers --> </SCRIPT> </HEAD> <BODY> <H1>Validating Form Input</H1> <FORM ACTION="lwapp.cgi" METHOD="post"> Quantity of tennis balls? <INPUT TYPE="text" NAME="quantity" onFocus="foc()" onBlur="blu()" onChange="qty_check(this, 0, 999)"> <BR> <INPUT TYPE="button" VALUE="Enter Order" onClick="validateAndSubmit(this.form)"> </FORM> </BODY> Try it

Using Windows and Frames

Can create a window with the open method"color.html") Can specify attributes such as window's height and width and whether window contains toolbar, location field, or scrollbars ("", "purduePlace", "height=300,width=500,location=yes, toolbar=no,scrollbars=yes") Try it

function Navigator() { myWin= open("Navigation.html", "displayWindow", "width=250,height=120,status=no, toolbar=no,menubar=no"); } <BODY BGCOLOR="#000000" OnLoad="Navigator()"> Try it

Closing windows and creating a back button (this one opens in a new window by using TARGET="_blank")

Closing windows and creating a back button (this one opens in the same window)

Creating a form with a selected mailto that opens a window

Creating a Frame

<FRAMESET ROWS="90%,10%"> <FRAMESET COLS="30%,70%"> <FRAME SRC=category.html NAME="listFrame"> <FRAME SRC=titles.html NAME="contentFrame"> </FRAMESET> <FRAME SRC=navigate.html NAME="navigateFrame"> </FRAMESET> listFrame is top.frames[0]
contentFrame is top.frames[1]
navigateFrame is top.frames[2]

function reframe() { top.frames[0].location='inter.title.html'; top.frames[1].location='inter.toc.html'; top.frames[2].location='titlePage.html'; } <INPUT TYPE="button" VALUE="The Internet" onClick="reframe()"> Try it

Using JavaScript URLs

function visit() { if (confirm ("Would you like to visit Purdue?")) ("", "purduePlace", "height=300,width=500,location=yes, toolbar=no,scrollbars=yes") else alert("Maybe next time...") } This page can open a new window containing the <A HREF="javascript:visit()"> Purdue Website</A>....<P> Try it