Conditional statements are used to perform different actions
based on different conditions.
Conditional Statements
Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.In JavaScript we have the following conditional statements:
- if statement - use this statement to execute some code only if 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 false
- if...else if....else statement - use this statement to select one of many blocks of code to be executed
- switch statement - use this statement to select one of many blocks of code to be executed
If Statement
Use the if statement to execute some code only if a specified condition is true.Syntax
if (condition)
{
code to be executed if condition is true
}
Note: (if) is written in lowercase letters. Using uppercase letters (IF)
will generate a JavaScript error!{
code to be executed if condition is true
}
<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<12)
{
document.write("<b>Good morning</b>");
}
</script>
//Write a "Good morning" greeting if
//the time is less than 10
var d=new Date();
var time=d.getHours();
if (time<12)
{
document.write("<b>Good morning</b>");
}
</script>
Example
<html>
<body>
<script type="text/javascript">
var d = new Date();
var time = d.getHours();
if (time < 12)
{
document.write("<b>Good morning</b>");
}
</script>
<p>This example demonstrates
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
Use the if....else statement to execute some code if a condition is true and another code if the condition is not true.condition
if (condition)
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}
syntax
<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 < 12)
{
document.write("Good morning!");
}
else
{
document.write("Good day!");
}
</script>
//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 < 12)
{
document.write("Good morning!");
}
else
{
document.write("Good day!");
}
</script>
Example
<html>
<body>
<script
type="text/javascript">
var d = new Date();
var time = d.getHours();
if (time < 10)
{
document.write("<b>Good
morning</b>");
}
else
{
document.write("<b>Good
day</b>");
}
</script>
<p>
This example demonstrates 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
Use the if....else if...else statement to select one of several blocks of code to be executed.condition
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 neither condition1 nor condition2 is true
}
{
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 neither condition1 nor condition2 is true
}
syntax
<script type="text/javascript">
var d = new Date()
var time = d.getHours()
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>
var d = new Date()
var time = d.getHours()
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
<html>
<body>
<script
type="text/javascript">
var d = new Date();
var time = d.getHours();
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 demonstrates the
if..else if...else statement.
</p>
</body>
</html>
JavaScript Switch Statement
Conditional statements are used to perform different actions
based on different conditions.
The JavaScript Switch Statement
Use the switch statement to select one of many blocks of code to be executed.condition
switch(n)
{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is different from case 1 and 2
}
This is how it works: First we have a single expression n (most often
a variable), that is evaluated once. The value of the expression is then
compared with the values for each case in the structure. If there is a match,
the block of code associated with that case is executed. Use break to
prevent the code from running into the next case automatically.{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is different from case 1 and 2
}
syntax
<script type="text/javascript">
//You will receive a different greeting based
//on what day it is. Note that Sunday=0,
//Monday=1, Tuesday=2, etc.
var d=new Date();
var theDay=d.getDay();
switch (theDay)
{
case 5:
document.write("Finally Friday");
break;
case 6:
document.write("Super Saturday");
break;
case 0:
document.write("Sleepy Sunday");
break;
default:
document.write("I'm looking forward to this weekend!");
}
</script>
//You will receive a different greeting based
//on what day it is. Note that Sunday=0,
//Monday=1, Tuesday=2, etc.
var d=new Date();
var theDay=d.getDay();
switch (theDay)
{
case 5:
document.write("Finally Friday");
break;
case 6:
document.write("Super Saturday");
break;
case 0:
document.write("Sleepy Sunday");
break;
default:
document.write("I'm looking forward to this weekend!");
}
</script>
Example
<html>
<body>
<script
type="text/javascript">
var d=new Date();
var theDay=d.getDay();
switch (theDay)
{
case 5:
document.write("<b>Finally Friday</b>");
break;
case 6:
document.write("<b>Super Saturday</b>");
break;
case 0:
document.write("<b>Sleepy Sunday</b>");
break;
default:
document.write("<b>I'm really looking forward to this
weekend!</b>");
}
</script>
<p>This JavaScript will
generate a different greeting based on what day it is. Note that Sunday=0,
Monday=1, Tuesday=2, etc.</p>
</body>
</html>
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