The while Loop

By Stephen Bucaro

A loop structure allows you execute a series of statements over and over. Several kinds of loop structures are available in Java Script, the while loop evaluates an expression, and while the expression evaluates to true, the while loop will repeatedly execute a series of statements. The syntax for the while loop is shown below.

while(condition)
{
   statements;
}

The Condition expression inside the brackets is evaluated. The result of that evaluation can be true or false. If the result is true the statements inside the curly brackets will be executed. If the result is false, the loop terminates and program flow continues with the next statement following the while loop structure.

var price = 10.00;

while(price > 5.00)
{
   price -= 1.00;
}

alert("The final price is: " + price);

In the example above, the variable price is initialized to 10.00. The Condition expression inside the while loop brackets tests the value of price to see if it's greater than 5.00. If the value of price is greater than 5.00, the statements inside the curly brackets are executed; 1.00 is subtracted from price. The condition expression again tests the value of price.

After the statements inside the curly brackets are executed five times, the value of price is no longer greater than 5.00. The result of the condition expression evaluation becomes false, the while loop terminates.

program flow continues with the next statement following the while loop structure, which creates a message box displaying the final value of price (5.00).

The do/while Loop

A structure closely related to the while loop is the do/while loop. The syntax for the do/while loop is shown below.

do
{
   statements;

}
while(condition);