Java Script Part 1
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Client-Side programming
with JavaScript 2
Event-driven programs and HTML
form elements
Event-driven programs and HTML form elements
event-driven programs
onload, onunload
HTML forms & attributes
button, text box, text area
selection list, radio button, check box, password, hidden,
…
JavaScript form events
properties: name, type, value, …
methods: blur(), focus(), click(), …
event handlers: onblur(), onfocus(), onchange(), onclick(),
…
advanced features & techniques
windows & frames, timeouts, cookies
Event-driven programs
• Computation within a Web page is rarely serial instead,
the page reacts to events such as mouse clicks, buttons, …
much of JavaScript's utility is in specifying actions that
are to occur in the page as a result of some event
the programmer may have little or no control over
when code will (if ever) be executed, e.g., code that
reacts to a button click
there is no set sequence, the page waits for events and
reacts
OnLoad & OnUnload
•the simplest events are when the page is
loaded or unloaded
–the onload attribute of the <body> tag
specifies JavaScript code that is automatically
executed when the page is loaded
–the onunload attribute similarly specifies
JavaScript code that is automatically
executed when the browser leaves the page
<html>
<head>
<title>Hello/Goodbye page</title>
<script type="text/javascript">
function Hello()
{
globalName=prompt("Welcome to my page. "
+"What is your name?","");
}
function Goodbye()
{
alert(“Goodbye, " + globalName +
" come back real soon.");
}
</script>
</head>
<body onload="Hello();" onunload="Goodbye();">
Whatever text appears in the page.
</body>
</html>
view page
HTML forms
• most event-handling in JavaScript is associated with form
elements
• an HTML form is a collection of elements for handling input,
output, and events in a page
<form name="FormName">
…
</form>
form elements might include:
for input:
button, selection list, radio button, check box,
password, …
for input/output: text box, text area, …
Button Element
• the simplest form element is a button
–analogous to a real-world button, a click
can be used to trigger events
<input type="button"
value="LABEL"
onclick="JAVASCRIPT_CODE"/>
<html>
<head>
<title> Fun with Buttons</title>
<script type="text/javascript“ src="random.js">
</script>
</head>
<body>
<form name="ButtonForm">
<input type="button" value="Click for Lucky
Number"
onclick= “var num = RandomInt(1, 100);
alert('The lucky number for the day is ' + num);"
>
</form>
</body>
</html>
view page
Buttons & Functions
for complex tasks, should define function(s) and have the onclick event trigger a
function call
<html>
<head>
<title>Fun with Buttons</title>
<script type="text/javascript">
function Greeting()
// Results: displays a time-sensitive greeting
{
var now = new Date();
if (now.getHours() < 12) {
alert("Good morning");
}
else if (now.getHours() < 18) {
alert("Good afternoon");
}
else {
alert("Good evening");
}
}
</script>
</head>
<body>
<form name="ButtonForm">
<input type="button" value="Click for Greeting"
onclick="Greeting();" >
</form>
</body>
</html>
view page
Text Boxes
• a text box allows for user input
– unlike prompt, user input persists on the page & can be
edited
<input type="text" name=“UserName"… />
optional attributes:
size : width of the box (number of characters)
value : initial contents of the box
Maxlength: Specify the maximum input length
JavaScript code can access the contents as
document.BoxForm.userName.value
Text Boxes
<html>
<head>
</head>
<title> Fun with Text Boxes </title>
<body>
<form name="BoxForm">
Enter your name here:
<input type="text" name="userName"
size=“12” value="" >
<br /><br />
<input type="button" value="Click Me"
onclick="alert('Thanks, ' +
document.BoxForm.userName.value +
', I needed that.');" >
</form>
</body>
</html>
view page
Read/Write Text Boxes
• similarly, can change the contents with an
assignment
Note: the contents are raw text, no HTML
formatting
Also: contents are accessed as a string, must
parseFloat or parseInt if want a
number
Read/Write Text Boxes
<html>
<head>
<title> Fun with Text Boxes </title>
</head>
<body>
<form name="BoxForm">
Enter a number here:
<input type="text" size=“12” name="number" value=“2”
/>
<br /><br />
<input type="button" value="Double"
onclick="document.BoxForm.number.value=
parseFloat(document.BoxForm.number.value) * 2;" />
</form>
</body>
</html>
view page
Text Box Events
•onchange triggered when the contents of
the box are changed
•onfocus triggered when the mouse clicks in
the box
•blur() removes focus
Text Box Events
<html>
<head>
<title> Fun with Text Boxes </title>
<script type="text/javascript">
function FahrToCelsius(tempInFahr)
// Assumes: tempInFahr is a number
//(degrees Fahrenheit)
// Returns: corresponding temperature in
//degrees Celsius
{
return (5/9)*(tempInFahr - 32);
}
</script>
</head>
Text Box Events
<body>
<form name="BoxForm">
Temperature in Fahrenheit:
<input type="text" name="Fahr" size=“10” value=“0"
onchange="document.BoxForm.Celsius.value =
FahrToCelsius(parseFloat(document.BoxForm.Fahr.value));" >
&nbsp; ---- &nbsp;
<input type="text" name="Celsius" size=“10” value=""
onfocus="blur();" >
in Celsius
</form>
</body>
view page
</html>
Text Box Validation
• what if the user enters a non-number in the
Fahrenheit box?
• solution: have the text box validate its own contents
– start with legal value
– at onchange, verify that new value is legal
(otherwise, reset)
– the verify.js library defines several functions
for validating text boxes
Text Box Validation
function VerifyNum(textBox)
// Assumes: textBox is a text box
// Returns: true if textBox contains a number, else false +
alert
{
var boxValue = parseFloat(textBox.value);
if ( isNaN(boxValue) ) {
// ** isNaN function
alert("You must enter a number value!");
textBox.value = "";
return false;
}
return true;
}
Validation Example
<html>
<head>
<title> Fun with Text Boxes </title>
<script type="text/javascript"
src="verify.js">
</script>
<script type="text/javascript">
function FahrToCelsius(tempInFahr)
{
return (5/9)*(tempInFahr - 32);
}
</script>
</head>
Validation Example
<body>
<form name="BoxForm">
Temperature in Fahrenheit:
<input type="text" name="Fahr" size=“10” value=“0”
onchange="if (VerifyNum(this)) { // this refers to current element
document.BoxForm.Celsius.value =
FahrToCelsius(parseFloat(this.value));
}" >
&nbsp; &nbsp;
<input type="text" name="Celsius" size=“10” value=""
onfocus="blur();" >
in Celsius
</form>
</body>
</html>
view page
OnSubmit
• The OnSubmit event is used to validate ALL form fields
before submitting it.
<form method="post" action=“MMM.htm“
onsubmit="return checkForm()">
The function checkForm() returns either true or false. If it
returns true the form will be submitted, otherwise the submit
will be cancelled
JavaScript indexOf() Method
• Definition and Usage
• The indexOf() method returns the position of the first
occurrence of a specified string value in a string.
• Syntax
– stringObject.indexOf(searchvalue)
• The indexOf() method is case sensitive!
Validation Example
<body>
<form action="submitpage.htm"
onsubmit="return validate_form(this)"
method="post">
Email: <input type="text" name="email" size="30">
<input type="submit" value="Submit">
</form>
</body>
Validation Example
•
Required Fields:
function validate_required(field , alerttxt)
{
with (field)
{
if (value==null || value=="")
{alert(alerttxt)
return false}
else
{return true}
}
}
view page
JavaScript Email Validation
function validate_form(thisform)
{
with (thisform)
{
if (validate_required(email,"Email must be filled out!")==false)
{email.focus()
return false
}
}
}
JavaScript Email Validation
function validate_email(field , alerttxt)
{
with (field)
{apos=value.indexOf("@")
dotpos=value.lastIndexOf(".")
if (apos<1||dotpos-apos<2)
{
alert(alerttxt)
return false
}
else
{return true}
}
}
view page
JavaScript Animation
<a href="http://www.Google.com"
target="_blank“
onmouseOver="mouseOver()“
onmouseOut="mouseOut()">
<img border="0" alt="Visit
Google!"src="b_pink.gif" name="b1" />
</a>
JavaScript Animation
<script type="text/javascript">
function mouseOver()
{
document.b1.src ="b_blue.gif“
}
function mouseOut()
{
document.b1.src ="planets.gif “
}
</script>
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Text Areas
• a TEXT box is limited to one line of input/output
• a TEXTAREA is similar to a text box in
functionality, but can specify any number of rows
and columns
<textarea name="TextAreaName"
rows=“NumRows” cols=“NumCols”>
Initial Text
</textarea>
Text Areas
–Note: unlike a text box, a TEXTAREA has
a separate closing tag
• initial contents of the TEXTAREA appear
between the tags
–as with a text box, no HTML formatting of
TEXTAREA contents
TEXTAREA Example
<html>
<head>
<title> Fun with Textareas </title>
<script type="text/javascript“ src="verify.js">
</script>
<script type="text/javascript">
function Table(low, high, power)
{// Results: displays table of numbers between low &
//high, raised to power
var message = "i: i^" + power + "\n-------\n";
for (var i = low; i <= high; i++) {
message = message + i + ": " + Math.pow(i,
power) + "\n";
}
document.AreaForm.Output.value = message;
}
</script>
</head>
<body>
<form name="AreaForm">
<div style="text-align: center;">
Show the numbers from <input type="text" name="lowRange"
size=“4” value=“1” onchange="VerifyInt(this);" />
to <input type="text" name="highRange" size=“4” value=“10”
onchange="VerifyInt(this);" />
raised to the power of <input type="text" name="power" size=3
value=2 onchange="VerifyInt(this);" />
<br /> <br />
<input type="button" value="Generate Table"
onClick="Table(parseFloat(document.AreaForm.lowRange.value),
parseFloat(document.AreaForm.highRange.value),
parseFloat(document.AreaForm.power.value));" />
<br /> <br />
<textarea name="Output" rows=“20” cols=“15”></textarea>
</div>
</form>
</body>
</html>
view page
Better (and easier?) methods to access
data
• So far, we have been accessing data input fields by giving them
names, and using the “dotted” names from the Document Object
Model tree structure.
• What if someone modifies the HTML document?
• Then, all those multiply referenced items can no longer be
accessed.
• A more reliable manner (more resistant to changes in the
webpage code) would be to give each element an ID (using the
“id” attibute) and use the JavaScript getElementById method.
Using getElementById
<html>
<head>
<title> Fun with Text Boxes </title>
<script type="text/javascript"
src="verify.js">
</script>
<script type="text/javascript">
function FahrToCelsius(tempInFahr)
{
return (5/9)*(tempInFahr - 32);
}
</script>
</head>
Using getElementById
<body>
<form name="BoxForm">
Temperature in Fahrenheit:
<input type="text" id="Fahr" size=“10” value=“0”
onchange="if (VerifyNum(this)) { // this refers to current element
var F=document.getElementById(‘Fahr’);
document.BoxForm.Celsius.value =
FahrToCelsius(parseFloat(F.value));
}" />
&nbsp; <tt>----></tt> &nbsp;
<input type="text" name="Celsius" size=“10” value=“”
onfocus=“getElementById(‘F’).focus();" />
in Celsius
</form> </body>
</html>
view page
Check buttons
<html>
<head>
<title> Check Boxes </title>
<script type="text/javascript">
function processCB()
{var boxes = document.BoxForm.cb.length;
var s="";
for (var i = 0; i < boxes; i++)
{
if (document.BoxForm.cb[i].checked)
{ s = s + document.BoxForm.cb[i].value + " "; }
}
if (s == "") { s = "nothing"; }
alert("You selected " + s);
}
</script>
</head>
Check buttons
<body>
<form name="BoxForm">
Which of these things is unavoidable in life (select one
or more):<br/><br/>&nbsp;
<input type="checkbox" name="cb“ value="Death">Death
</input><br/>&nbsp;
<input type="checkbox" name="cb"
value="Taxes">Taxes</input><br/> &nbsp;
<input type="checkbox" name="cb" value=“Watching TV">
Watching TV </input><br>
<br>
<input type="button" value="Done" onclick="processCB()“
>
</form>
</body>
</html>
view page
Radio buttons
• Radio buttons are similar to check boxes, but
only one of them can be selected at any time.
• They are defined by <input type=“radio”>
tags (similar to the checkbox tags in the
previous example, with similar properties)
and accessed in the same manner.
view page
JavaScript & Timeouts
• the setTimeout function can be used to
execute code at a later time
setTimeout(JavaScriptCodeToBeExecuted,
MillisecondsUntilExecution)
• example: forward link to a moved page
<html>
<head>
<title> Fun with Timeouts </title>
<script type="text/javascript">
function Move()
// Results: sets the current page //contents to be
newhome.html
{
self.location.href = "newhome.html";
}
</script>
</head>
<body onload="setTimeout('Move()', 3000);">
This page has moved to <a
href="newhome.html">newhome.html</a>.
</body>
</html>
view page
Another Timeout Example
<html>
<head>
<title> Fun with Timeouts </title>
<script type="text/javascript">
function timeSince()
// Assumes: document.CountForm.countdown exists in the page
// Results: every second, recursively writes current countdown
//in the box
{
// CODE FOR DETERMINING NUMBER OF DAYS, HOURS, MINUTES, AND
//SECONDS
// UNTIL GRADUATION (see the file for this code!!!)
document.CountForm.countdown.value=
days + " days, " + hours + " hours, " +
minutes + " minutes, and " + secs + " seconds";
setTimeout("timeSince();", 1000);
}
</script>
</head>
Another Timeout Example
<body onload="timeSince();">
<form name="CountForm">
<div style="text-align: center;">
Countdown to Graduation 2015 <br />
<textarea name="countdown" rows=“4” cols=“15”
style="font-family: Courier;" onfocus="blur();"></textarea>
</div>
</form>
</body>
</html>
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