JavaScript Condition

Like many other programming languages, JavaScript also allows you to write code that performs different actions based on the results of a logical or comparative test conditions at run time. This means you can create test conditions in the form of expressions that evaluates to either true or false and based on these results you can perform certain actions.

There are several conditional statements in JavaScript that you can use to make decisions:

• The if statement
• The if...else statement
• The if...else if....else statement
• The switch...case statement

We will discuss each of these statements in detail in the coming sections.

The if Statement

The if statement is used to execute a block of code only if the specified condition evaluates to true. This is the simplest JavaScript's conditional statements and can be written like:

if(condition) {
    // Code to be executed
}

The following example will output "Have a nice weekend!" if the current day is Friday:

Example

var now = new Date();

var dayOfWeek = now.getDay(); // Sunday - Saturday : 0 - 6 

if(dayOfWeek == 5) {

    alert("Have a nice weekend!");

}

 

The if...else Statement

You can enhance the decision making capabilities of your JavaScript program by providing an alternative choice through adding an else statement to the if statement.

The if...else statement allows you to execute one block of code if the specified condition is evaluates to true and another block of code if it is evaluates to false. It can be written, like this:

if(condition) {
    // Code to be executed if condition is true
} else {
    // Code to be executed if condition is false
}

The JavaScript code in the following example will output "Have a nice weekend!" if the current day is Friday, otherwise it will output the text "Have a nice day!".

Example

var now = new Date();

var dayOfWeek = now.getDay(); // Sunday - Saturday : 0 - 6

if(dayOfWeek == 5) {

    alert("Have a nice weekend!");

} else {

    alert("Have a nice day!");

}

 

The if...else if...else Statement

The if...else if...else a special statement that is used to combine multiple if...else statements.

if(condition1) {
    // Code to be executed if condition1 is true
} else if(condition2) {
    // Code to be executed if the condition1 is false and condition2 is true
} else {
    // Code to be executed if both condition1 and condition2 are false
}

The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday, otherwise it will output "Have a nice day!"

Example

var now = new Date();

var dayOfWeek = now.getDay(); // Sunday - Saturday : 0 - 6

 if(dayOfWeek == 5) {

    alert("Have a nice weekend!");

} else if(dayOfWeek == 0) {

    alert("Have a nice Sunday!");

} else {

    alert("Have a nice day!");

}

You will learn about the JavaScript switch-case statement in the next chapter.

 

The Ternary Operator

The ternary operator provides a shorthand way of writing the if...else statements. The ternary operator is represented by the question mark ( ? ) symbol and it takes three operands: a condition to check, a result for true , and a result for false . Its basic syntax is:

var result = (condition) ? value1 : value2

If the condition is evaluated to true the value1 will be returned, otherwise value2 will be returned. To understand how this operator works, consider the following examples:

Example

var userType;

var age = 21;

if(age < 18) {

    userType = 'Child';

} else {

    userType = 'Adult';

}

alert(userType); // Displays Adult

Using the ternary operator the same code could be written in a more compact way:

Example

var age = 21;

var userType = age < 18 ? 'Child' : 'Adult';

alert(userType); // Displays Adult

As you can see in the above example, since the specified condition evaluated to false the value on the right side of the colon ( : ) is returned, which is the string 'Adult'.

Tip: Code written using the ternary operator can be difficult to read sometimes. However, it provides a great way to write compact if-else statements.