HTML and CSS Reference
In-Depth Information
The body of the loop just prints out a message that includes the value of count each time
through the loop.
As you can see, the for statement is self-contained. The count
variable is declared, tested, and incremented within that state-
ment. You shouldn't modify the value of count within the body of
your loop unless you're absolutely sure of what you're doing.
while Loops
The basic structure of a while loop looks like this:
var color = 'blue';
while (color == 'blue') {
document.write(“Color is still blue.”);
if (Math.random() > 0.5) {
color = 'not blue';
The while loop uses only a condition. The programmer is responsible for creating the
condition that will eventually causes the loop to terminate somewhere inside the body of
the loop. It might help you to think of a while loop as an if statement that's executed
repeatedly until a condition is satisfied. As long as the while expression is true, the state-
ments inside the braces following the while loop continue to run forever—or at least
until you close your web browser.
In the preceding example, I declare a variable, color , and set its value to “blue” . The
while loop will execute until it is no longer true that color is set to “blue” . Inside
the loop, I print a message indicating that the color is still blue, and then I use an if
statement that may set the color variable to a different value. The condition in the
if statement uses Math.random() , which returns a value between 0 and 1 . In this case,
if it's greater than 0.5, I switch the value so that the loop terminates.
If you prefer, you can write while loops with the condition at the end, which ensures that
they always run once. These are called do ... while loops, and look like this:
var color = “blue”;
do {
// some stuff
while (color != “blue”);
Even though the test in the loop will not pass, it will still run once because the condition
is checked after the first time the body of the loop runs.
Search WWH ::

Custom Search