JavaScript If…Else Statements

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 that if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error!

<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&lt;10)
  {
  document.write(<b>Good morning</b>");
  }
</script>

Notice that there is no ..else.. in this syntax. You tell the browser to execute some codeĀ 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.

if (condition)
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}
<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>

If…else if…else Statement

Use the if….else if…else statement to select one of several blocks of code to be executed.

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 neither condition1 nor condition2 is true
}
<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>
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