javascript

The while Statement
Chapter 3: Language Basics
The while statement is a pretest loop. This means the escape condition is evaluated before the code
inside the loop has been executed. Because of this, it is possible that the body of the loop is never
executed. Here ’ s the syntax:
while(expression) statement
And here ’ s an example of its usage:
var i = 0;
while (i < 10) {
i += 2;
}
In this example, the variable i starts out equal to 0 and is incremented by two each time through the
loop. As long as the variable is less than 10, the loop will continue.
The for Statement
The for statement is also a pretest loop with the added capabilities of variable initialization before
entering the loop and defining postloop code to be executed. Here ’ s the syntax:
for (initialization; expression; post-loop-expression) statement
And here ’ s an example of its usage:
var count = 10;
for (var i=0; i < count; i++){
alert(i);
}
This code defines a variable i that begins with the value 0. The for loop is entered only if the
conditional expression ( i < count ) evaluates to true , making it possible that the body of the code
might not be executed. If the body is executed, the postloop expression is also executed, iterating the
variable i . This for loop is the same as the following:
var count = 10;
var i = 0;
while (i < count){
alert(i);
i++;
}
Nothing can be done with a for loop that can ’ t be done using a while loop. The for loop simply
encapsulates the loop - related code into a single location.
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