While writing a
program, you may encounter a situation where you need to perform an action over
and over again. In such situations, you would need to write loop statements to
reduce the number of lines.
The while Loop
The most basic loop in
JavaScript is the while loop which
would be discussed in this chapter. The purpose of a while loop is to execute a statement or code block repeatedly as
long as an expression is true. Once
the expression becomes false, the
loop terminates.
Flow Chart
The flow chart of while loop
looks as follows:
Syntax
The syntax of while loop in
JavaScript is as follows:
while
(expression){
Statement(s) to be
executed if expression is true
}
Example
Try the following example to implement while loop.
<html>
<body>
<script
type="text/javascript">
<!--
var count = 0;
document.write("Starting
Loop ");
while (count <
10){
document.write("Current
Count : " + count + "<br />");
count++;
}
document.write("Loop
stopped!");
//-->
</script>
<p>Set the
variable to different value and then try...</p>
</body>
</html>
Output
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Current Count : 5
Current Count : 6
Current Count : 7
Current Count : 8
Current Count : 9
Loop stopped!
Set the variable
to different value and then try...
The do...while Loop
The do...while loop is similar to the while loop except that the condition check
happens at the end of the loop. This means that the loop will always be
executed at least once, even if the condition is false.
Flow Chart
The flow chart of a do-while
loop would be as follows:
Syntax
The syntax for do-while
loop in JavaScript is as follows:
do{
Statement(s) to be
executed;
} while
(expression);
Note: Don’t miss
the semicolon used at the end of the
do...while loop.
Example
Try the following example to learn how to
implement a do-while loop in
JavaScript.
<html>
<body>
<script
type="text/javascript">
<!--
var count = 0;
document.write("Starting
Loop" + "<br />");
do{
document.write("Current
Count : " + count + "<br />");
count++;
}while (count <
5);
document.write
("Loop stopped!");
//-->
</script>
<p>Set the
variable to different value and then try...</p>
</body>
</html>
Output
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Loop Stopped!
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