Conditional Statements in JavaScript

Thomas Valentine

Conditional Statements give the JavaScript code you are writing the ability to make decisions or perform single or multiple tasks. These Conditional statements were borrowed from older, more polished languages like C, C++, and Java. Porting over the functionality of these very capable languages gives JavaScript a very polished set of useful and functionally correct tools which you, the developer, can work with.

A conditional statement uses the operators that were discussed in an earlier chapter. There are three conditionals used within the JavaScript language, which will be discussed in depth in the coming sections. They are as follows.

• The if and if / else Conditional Statements
• The else / if Conditional Statement
• The switch / case Conditional Statement

The If and If/Else Conditional Statements

if (expression)
   statement; 

The example shows the if keyword followed by an expression within brackets. Within these brackets are the conditions that must be met in order to execute the statement. If the condition is never met, the statement is never executed. Simply put, the expression must evaluate to true in order for the statement to be executed. Within this simple conditional are an infinite number of variations. Basically, you're letting the script make decisions based on the condition, the expression, you supply.

While performing an action if a value of true is returned from the expression is great, you will eventually have a need for something to happen if the expression evaluates to false. Assigning an action to the false output of the expression involves a very simple addition to the if statement given above. The else keyword is used to supply an action to be taken if the expression is false. Examine the syntax example below.

if (expression) {
   statement If expression is True;
   } else {
   statement If expression is False;
} 

The Conditional Operator
The JavaScript Chronicles
The if and if/else Conditional Statements - Page 2

The JavaScript Chronicles