Very often once you write
code, you want to perform different actions for various decisions.
you'll use conditional statements in your code to do to to the
present.
In JavaScript we have the next conditional statements:
• if statement - use this statement to execute some code as long as a
specified condition is true.
• if...else statement - use this statement to execute some code if the
condition is true and another code if the condition is fake.
• if...else if....else statement - use this statement to choose one all
told many blocks of code to be executed.
• switch statement - use this statement to select out one of many
blocks of code to be executed.
If Statement
Use the if statement to execute some code on condition that 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
<script
type="text/javascript">
//Write a "Good morning" greeting if
//the time is less than 10
var d=new Date();
var time=d.getHours();
if (time<10)
{
document.write("<b>Good morning</b>");
}
</script>
Notice that there is no ..else.. in this syntax. You tell the browser to
execute some code only if the specified condition is true.
If...else Statement
Use
the if....else statement to execute some code if a condition is true and
another code if the condition is not true.
Syntax
if
(condition)
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}
Example
<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>
Switch Statement
Use
the switch statement to select one of many blocks of code to be executed. It is
multi way decision making statement.
Syntax
switch(expression)
{
case value 1:
statement 1;
break;
case value 2:
statement 2;
break;
………………..
………………..
default:
default statement;
}
Example
<html>
<body>
<script type="text/javascript">
var letter="U";
switch(letter)
{
case"A":
document.write("A is vowel");
break;
case"E":
document.write("E is vowel ");
break;
case"I":
document.write("I is vowel ");
break;
case"O":
document.write("O is vowel ");
break;
case"U":
document.write("U is vowel ");
break;
default:
document.write("Letter is consonant");
}
</script>
</body>
</html>