JavaScript Conditional Statement


JavaScript if...else Statement

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


Conditional Statements

Usually when writing code, you always need to perform different actions for different decisions. You can use conditional statements in your code to accomplish this task.

In JavaScript, we can use the following conditional statements:

  • if statement - Only when the specified condition is true, use this statement to execute the codes

  • if...else statement - Executes codes when the condition is true, executes other codes when the condition is false

  • if...else if...else statement - Use this statement to select one of multiple code blocks to execute

  • switch statement - use this statement to select one of multiple codes blocks to execute


if Statement

Only when the specified condition is true, the statement will execute the codes.

Grammar

if ( condition )
{
    code executed when the condition is true
}

Please use lowercase if . Using capital letters (IF) will generate a JavaScript error!

Example

When the time is less than 20:00, the greeting "Good day" is generated:

if (time<20)
{
     x="Good day";
}

The x result is: Good day

 Try It! 

Please note that there is no ...else... in codes. You have told the browser to execute the codes only when the specified condition is true.


if...else Statement

Please use if...else statement to execute codes when the condition is true, and execute other codes when the condition is false.

Grammar

if ( condition )
{
    codes is executed when the condition is true
}
else

    codes is executed when the condition is not true
}

Example

When the time is less than 20:00, the greeting "Good day" is generated, otherwise the greeting "Good evening" is generated.

if (time<20)
{
     x="Good day";
}
else
{
     x="Good evening";
}

The x result is: Good day

 Try It! 


if ... else if ... else Statement

Use if...else if...else statement to select one of multiple code blocks to execute.

Grammar

if ( condition1 )
{
    code executed when condition 1 is true
}
else if ( condition2 )
{
    code executed when condition 2 is true
}
else

    code executed when condition 1 and condition 2 are neither true
}

Example

If the time is less than 10:00, the greeting "Good morning" is generated.

If the time is greater than 10:00 and less than 20:00, the greeting "Good day" is generated

Otherwise the greeting "Good evening" is generated:


if (time<10)
{
     document.write("<b>Good morning</b>");
}
else if (time>=10 && time<20)
{
     document.write("<b>Good today</b>");
}
else
{
     document.write("<b>Good evening!</b>");
}

The x result is: Good evening

 Try It! 


Examples

More Examples

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