Conditional Statements

Conditional statements are used to perform different actions based on different conditions.

JavaScript supports the following conditional statements:

• if - execute some code only if a specified condition is true
• if...else - execute some code if the condition is true and another code if the condition is false
• if...else if...else - select one of many blocks of code to be executed
• switch - select one of many blocks of code to be executed

if statement

The if statement is used to execute some code only if a specified condition is true.

The if statement has the following syntax:

if (condition)
{
  executed if condition is true;
  }

The following example shows the basic use of the if statement.

<script>
//Write a "Good morning" if
//the time is less than 12

var d = new Date();
var hour = d.getHours();
if (hour < 12)
{
  document.write("Good morning");
}
</script>

if...else statement

The if...else statement is used to execute some code only if a specified condition is true and some other code if the condition is false.

The if...else statement has the following syntax:

if (condition)
{
  executed if condition is true;
  }
else
{
  executed if condition is false;
  }

The following example shows the basic use of the if...else statement.

<script>
//Write a "Good morning" if
//the time is less than 12
//Otherwise, write "Good day"

var d = new Date();
var hour = d.getHours();
if (hour < 12)
{
  document.write("Good morning");
}
else
{
  document.write("Good day");
}
</script>

if...else if...else statement

The if...else if...else statement to select one of several blocks of code to be executed.

The if...elseif...else statement has the following syntax:

if (condition)
{
  executed if condition is true;
}
elseif (condition)
{
  executed if condition is true;
}
else
{
  executed if condition is false;
}

The following example shows the basic use of the if...elseif...else statement.

<script>
//Write a "Good morning" if
//the time is less than 12
//Write a "Good afternoon" if
//the time is greater than 12
//and less than 18
//Otherwise, write "Good day"

var d = new Date();
var hour = d.getHours();
if (hour < 12)
{
  document.write("Good morning");
}
else if (hour > 12 && hour < 18)
{
  document.write("Good afternoon");
}
else
{
  document.write("Good day");
}
</script>

switch statement

The switch statement is used to perform different actions based on different conditions.

The switch statement has the following syntax:

switch (n)
{
  case 1:
    execute code block 1
    break;
  case 2:
    execute code block 2
     break;
  default:
    executed if n is not equal to
        case 1 or case 2
    }  

The following example shows the basic use of the switch statement.

<script>
var d = new Date();
dayOfWeek = d.getDay();
switch (dayOfWeek)
{
  case 5:
    document.write("TGIF");
    break;
  case 6:
  case 0:
    document.write("Party Time");
    break;
  case 1:
    document.write("Back to work");
    break;
  default:
    document.write("Waiting for the weekend");
}
</script>