While writing a program, there may be a situation when you need to
perform some action over and over again. In such situation you would
need to write loop statements to reduce the number of lines.
JavaScript supports all the necessary loops to help you on all steps of programming.
The while Loop
The most basic loop in JavaScript is the
while loop which would be discussed in this tutorial.
Syntax:
while (expression){
Statement(s) to be executed if expression is true
}
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The purpose of a
while loop is to execute a statement or code block repeatedly as long as
expression is true. Once expression becomes
false, the loop will be exited.
Example:
Following example illustrates a basic while loop:
<script type="text/javascript">
<!--
var count = 0;
document.write("Starting Loop" + "<br />");
while (count < 10){
document.write("Current Count : " + count + "<br />");
count++;
}
document.write("Loop stopped!");
//-->
</script>
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This will produce following result:
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!
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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.
Syntax:
do{
Statement(s) to be executed;
} while (expression);
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Note the semicolon used at the end of the
do...while loop.
Example:
Let us write above example in terms of
do...while loop.
<script type="text/javascript">
<!--
var count = 0;
document.write("Starting Loop" + "<br />");
do{
document.write("Current Count : " + count + "<br />");
count++;
}while (count < 0);
document.write("Loop stopped!");
//-->
</script>
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This will produce following result:
Starting Loop
Current Count : 0
Loop stopped!
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