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Lesson 14
JAVA SCRIPTING (CONTINUED....)
We can also get the result of addition or subtraction written on a page using `write' function
of the document object. Again we need to do a slight modification in the code as shown
below.
<HTML>
<script language="JavaScript">
<!--
function Addit()
{
var num1=document.Calform.One.value;
var num2=document.Calform.Two.value;
document.write("The result of this addition is " +
(parseFloat(num1)+parseFloat(num2))); }
function minus()
{ var num1=document.Calform.One.value; var num2=document.Calform.Two.value; document.write("The
result of this subtraction is " + (parseFloat(num1)
parseFloat(num2)));
}
//-->
</script>
<BODY>
<FORM name="Calform">
<P>
First Number:<INPUT TYPE="TEXT" NAME="One" maxlength="3">
<P>
Second Number:<INPUT TYPE="TEXT" NAME="Two" maxlength="3">
<P>
<INPUT TYPE="button" NAME="Add" VALUE="Add Them!!" onclick="Addit()">
<INPUT TYPE="button" NAME="Minus" VALUE="Subtract Them!!"
onclick="minus()">
<INPUT TYPE="RESET" VALUE="Reset!">
</FORM> </BODY>
</HTML>
When a user types 3 and 9 in the two text boxes, respectively, as shown in Fig. 1 below and
presses `AddThem!!' the addition of two nos. `12' is written on a web page (Fig. 2). On
clicking `Subtract Them!!' the subtraction of two nos. `-6' is written on a page (Fig. 3). Note
that in the brackets of `document.write' we concatenate or join some text information called
string (within double quotation marks) with the addition/subtraction of two nos. using `+' sign. The
addition/subtraction of nos. is achieved using function `parseFloat()', that is, a function of predefined global
object.
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Fig. 1
Fig. 2
Fig. 3
Multiply and divide calculator
See the following code:
<HTML>
<script language="JavaScript">
<!--
function Multiplyit()
{
var num1=document.Calform.One.value; var num2=document.Calform.Two.value;
alert(parseFloat(num1)*parseFloat(num2));
}
function Divideit()
{ var num1=document.Calform.One.value; var num2=document.Calform.Two.value;
alert(parseFloat(num1)/parseFloat(num2));
}
//-->
</script>
<BODY><h2> Multiply and Divide Calculator</h2>
<FORM name="Calform">
<P>
First Number:<INPUT TYPE="TEXT" NAME="One" maxlength="3">
<P>
Second Number:<INPUT TYPE="TEXT" NAME="Two" maxlength="3">
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<P>
<INPUT TYPE="button" NAME="Multiply" VALUE="Multiply"
onclick="Multiplyit()">
<INPUT TYPE="button" NAME="Divide" VALUE="Divide" onclick="Divideit()">
<INPUT TYPE="RESET" VALUE="Reset!">
</FORM>
</BODY>
</HTML>
Results are shown in Figures 4 and 5 below.
Fig. 4
Fig. 5
Example - A Drop-Down List of Links
<HTML>
<HEAD>
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<TITLE>A Drop-Down List of Links</TITLE>
</HEAD>
<SCRIPT LANGUAGE="JavaScript" TYPE="text/javascript">
<!--
function GoToIt(list)
{ var selection = list.options[list.selectedIndex].value  if (selection != "None")
location.href =
selection
}
//-->
</SCRIPT>
<BODY>
<FORM>
<SELECT WIDTH="20" onChange="GoToIt(this)">
<OPTION VALUE="None">Select a page previously done --->
<OPTION VALUE="calculator.htm">Calculator
<OPTION VALUE="styles.htm">Style Sheet
<OPTION VALUE="forms.htm">Web Forms
<OPTION VALUE="tablemargin.htm">Table Margins
<OPTION VALUE="frames.htm">Frames
</SELECT>
</FORM>
</BODY>
</HTML>
Result is shown in Fig. 6 below.
Fig. 6
In the above example, event handler `onchange' has been used, having the effect that when
an option is selected by the user the control is shifted to the above defined function
GoToIt(list). Due to the key word `this' information/list contained in the select tag is
available to the argument `list' of the function GoToIt(). When the function would be
executed the value of the selected option would be assigned to the variable `selection'. Due
to location.href=selection, the existing location of the web page is changed to the location of
the option/web page that has been selected and that particular web page opens. `Location' is
another
predefined
browser
object.
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Example - If Statement
IF statement in programming is used to alter the course of execution of code depending
upon the value of a condition. See the following example:
<HTML>
<script language="JavaScript">
<!--
function minus()
{
var num1=document.Calform.One.value;
var num2=document.Calform.Two.value;
if(parseFloat(num1)<parseFloat(num2))
{ alert("negative");
}
else
{
alert(parseFloat(num1)-parseFloat(num2));
}
}
//-->
</script>
<BODY> <FORM name="Calform"> <P> First Number:<INPUT TYPE="TEXT" NAME="One"
maxlength="3"> <P> Second Number:<INPUT TYPE="TEXT" NAME="Two" maxlength="3"> <P>
<INPUT TYPE="button" NAME="Minus" VALUE="Subtract" onclick="minus()">
<INPUT TYPE="RESET" VALUE="Reset!">
</FORM>
</BODY>
</HTML>
Results are shown in Figures 7 and 8 below.
Fig. 7
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Fig. 8
For LOOP
When we want some action to take place repeatedly till a particular point, we can apply a for
loop. General format is: for(initializationStatement;condition;updateStatement){statements}.
The code goes on executing itself till a certain condition is met.
Example
<HTML>
<HEAD>
<TITLE>Using the For Statement</TITLE>
</HEAD>
<BODY>
<SCRIPT>
<!--
for(i=1;i<7;i++) document.write("<H"+i+">Hello "+i+"!!</H"+i+">");
//->
</SCRIPT>
</BODY>
</HTML>
Result is shown in Fig. 9 below.
Fig. 9
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Note that using for loop we are able to generate six different levels of headings in HTML.
Some predefined JavaScript objects
A list of some commonly used predefined JavaScript object is given below: Global Array String Math Date
Global object is an object with globally-accessible variables/properties and functions. Netscape navigator
and internet explorer implement Global object, but do not allow it to be explicitly created or referenced.
Instead its properties and methods are referenced directly. NaN - `not a number' is one of its properties.
`parseFloat(string)' that parses the string as a floating point number, is the example of a function/method of
Global Object. Note a general difference between properties and functions of an object in that the names
of the properties are not followed by small brackets whereas the names of the functions do have small
brackets following their names. Information contained in the small brackets of a function is called
arguments. Also note that generally properties and functions of an object are invoked/referenced by typing
the name of the object followed by a dot before typing the property or function name, e.g,
document.write().
Array Object also has different properties and functions. `Length' is an important property of this object
that identifies the length of the array. Its methods/functions include
toString(), reverse(), sort() etc.
Array Example
<HTML>
<HEAD>
<TITLE>Using Arrays </TITLE>
</HEAD>
<BODY>
<H1>Using Arrays </H1>
<SCRIPT LANGUAGE="JavaScript" TYPE="text/javascript">
<!--
myArray=[0,1,2,3,4,5,6,7,8,9,10];
document.write("myArray: first element " +myArray[0]+"<P>");
document.write("myArray.toString(): "+myArray.toString()+"<P>");
document.write("myArray.join(':'): "+myArray.join(':')+"<P>");
document.write("myArray.reverse(): "+myArray.reverse()+"<P>");
document.write("myArray.sort(): "+myArray.sort()+"<P>");
//-->
</SCRIPT>
</BODY>
</HTML>
Result is shown in Fig. 10 below.
Fig. 10
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Math object provides a standard library of mathematical constants and functions. Following
example shows some properties and methods of this object.
<HTML>
<HEAD>
<TITLE>Using the Math object</TITLE>
</HEAD>
<BODY>
<H1>Using the Math object </H1>
<SCRIPT LANGUAGE="JavaScript" TYPE="text/javascript">
<!--
document.write("Math.PI :" +Math.PI +"<P>");
document.write("Math.LN2 :"+Math.LN2+"<P>");
document.write("Math.sin(90) :"+Math.sin(90)+"<P>");
document.write("Math.random() :"+Math.random()+"<P>");
document.write("Math.pow(2,3) :"+Math.pow(2,3)+"<P>");
document.write("Math.min(123,133): "+Math.min(123,133)+"<P>");
//-->
</SCRIPT>
</BODY>
</HTML>
Result is shown in Fig. 11 below.
Fig. 11
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