Conditional Statements

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

The if Statement

Use the if statement to specify a block of JavaScript code to be executed if a condition is true.

Syntax if(condition)
{
// block of code to be executed if the condition is true
}
Eg:
<script>
var x = 5;
if(x<10)
{
alert("x is less than 10."); /* This will be executed. */
}
</script>

The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax: if(condition)
{
// block of code to be executed if the condition is true
}
else
{
// block of code to be executed if the condition is false
}
Eg:
<script>
var fruit_name = "Orange";
if(fruit_name == "Apple")
{
alert("Fruit name is Apple");
}
else
{
alert("Fruit name is not Apple"); /* This will be executed. */
}
</script>

The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Syntax:
if(condition1)
{
// block of code to be executed if condition1 is true
}
else if(condition2)
{
// block of code to be executed if the condition1 is false and condition2 is true
}
else
{
// block of code to be executed if the condition1 is false and condition2 is false
}

Eg:
<script>
var x = 10;
if(x < 10)
{
alert("x is less than 10");
}
if(x == 10)
{
alert("x is equal to 10"); /* This will be executed. */
}
else
{
alert("x is greater than 10");
}
</script>

Switch Statement

Switch selects one of many blocks of code to be executed. The switch statement is used to avoid long blocks of if..elseif..else code.

switch (n)
{
case 1:
code to be executed if n=1;
break;
case 2:
code to be executed if n=2;
break;
case 3:
code to be executed if n=3;
break;
...
default:
code to be executed if n is different from all case labels;
}

Eg:
<script>
var fruit = "apple";
switch (fruit)
{
case "orange":
alert("Your fruit is orange!");
break;
case "apple":
alert("Your fruit is apple!"); // this will be executed
break;
case "banana":
alert("Your fruit is banana!");
break;
default:
alert("Your fruit is not orange, apple or banana!");
}
</script>