Conditional Statements
Very often
when you write code, you want to perform different actions for different
decisions. You can use conditional statements in our code to do this.
In
JavaScript we have the following conditional statements:
·
if statement - use this statement if you want to
execute some code if a specified condition is true.
·
If…else statement – use this statement if you
want to execute some code if the condition is true and another code if the
condition is false.
·
If….else if…else statement – use this statement
if you want to select one of many blocks of code to be executed
·
Switch statement – use this statement if you
want to select one of many blocks of code to be executed.
If Statement
You should
use the if statement if you want to execute some code only if a specified
condition is true.
Syntax
If (condition)
{
Code to be executed if condition is true
}
Note: that if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error!
Example 1
<script type=”text/javascript”>
//Write a “Good morning” greeting if
//the time is less thatn 10
Var d=new Date( )
Var time=d.get Houres( )
If (time<10)
{
Document.write(“<b>Good morning</b>”)
}
</script>
Example 2
<script type=”text/javascript”>
//Write “Lunch-time!” if the time is 11
Var d=new Date( )
Var time=d.get Houres( )
If (tim==<10)
{
Document.write(“<b>Lunch-time</b>”)
}
</script>
Note: When comparing variables you
must always use two equals signs next toeach other(= =)!
Notice that
there is no ..else.. in this syntax. You just tell the code to execute some
code only if the specified condition is true.
Example 3
<html>
<body>
<script type=”text/javascript”>
Var d=new Date( )
Var time=d.get Houres( )
If (time<10)
{
Document.write(“<b>Good morning</b>”)
}
</script>
<p>
This example demonstrate the If statement.
</p>
<p>
If the time on your browser is less than 10,
You will get a “Good morning” greeting.
</p>
</body>
</html>
If…else Statement
If you want
to execute some code if a condition is true and another code if the condition
is not true, use the if…else statement.
Syntax
If (condition)
}
Code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}
Example 1:
<script type=”text/javascript”>
//If the time is less than 10,
//you will get a “Good morning” greeting.
//Otherwise you will get a “Good Day” greeting.
var d = new date ( )
var time = d.getHours( )
if (time < 10)
{
Document.write (“Good morning!”)
}
else
{
Document.write (“Good day!”)
}
</script>
Example 2:
<html>
<body>
<script type=”text/javascript”>
var d=new Date( )
var time=d.getHoures( )
If (time<10)
{
Document.write(“<b>Good morning</b>”)
}
else
document.write(“<b>Good day</b>”)
}
</script>
<p>
This example demonstrate the If…Else statement.
</p>
<p>
If the time on your browser is less than 10,
you will get a “Good morning” greeting.
Otherwise you will get a “Good day” greeting.
</p>
</body>
</html>
If…else if…else Statement
You should
use the if….else if…if statement if you want to select one of many sets of
lines to execute.
Syntax
if (condition1)
{
Code to be executed if condition1 is true
}
Else if (condition2)
{
Code to be executed if condition2 is true
}
Else
{
Code to be executed if condition1 and condition2 are not
true
}
Example 1:
<script type=”text/javascript”>
var d=new Date( )
var time=d.getHoures( )
If (time<10)
{
Document.write(“<b>Good morning</b>”)
}
Else if (time>10 && time<16>
{
Document.write (“<b.Good day</b>”)
}
Else
{
Document.write(“<b>Hello World!</b>”)
}
</script>
Example 2:
<html>
<body>
<script type=”text/javascript”>
var d=new Date( )
var time=d.getHoures( )
If (time<10)
{
Document.write(“<b>Good morning</b>”)
}
else if (time>10 && time<16>
{
document.write (“<b.Good day</b>”)
}
else
{
document.write(“<b>Hello World!</b>”)
}
</script
<p>
This example demonstrate the if..else if… else statement.
</p>
</body>
</html>
Random link
This
example demonstrate a link, when you click on the link it will take you to
ulci.com.np OR to yahoo.com. There is a 50% chance for each of them.
Example:
<html>
<body>
<script type=”text/javascript”>
var r=Math.random( )
if (r>0.5)
{
Document.write (“<a
href= ‘http://www.ulci.com.np’)Universal
Lang.!
</a>”)
}
Else
{
document.write(“<a href=
‘http://www.yahoo.com’>Yahooooo….!</a>”)
}
</script>
</body>
</html>
