↑
Main Page

while

The

while

statement is a pretest loop. This means the evaluation of the escape condition is done before

the code inside the loop has been executed. Because of this, it is possible that the body of the loop is

never executed. Syntax:

while(

expression

)

statement

For example:

var i = 0;

while (i < 10) {

i += 2;

}

for

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 entered. Syntax:

for (

initialization

;

expression

;

post-loop-expression

)

statement

For example:

for (var i=0; i < iCount; i++){

alert(i);

}

This code defines a variable

that begins with the value

. The

for

loop is entered only if the conditional

expression (

i < iCount

) 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

for-in

The

for-in

statement is a strict iterative statement. It is used to enumerate the properties of an object.

Syntax:

for (

property

expression

)

statement

For example:

for (sProp in window) {

alert(sProp);

}

Here, the

for-in

statement is used to display all the properties of the BOM

window

object. The method

propertyIsEnumerable()

, discussed earlier, is included in ECMAScript specifically to indicate whether

or not a property can be accessed using the

for-in

statement.

ECMAScript Basics

05_579088 ch02.qxd 3/28/05 11:35 AM Page 55