ActionScript 2.0 Language Reference

Constants

A constant is a variable used to represent a property whose value never changes. This section describes global constants that are available to every script.

false Constant

When automatic data typing converts false to a number, it becomes 0; when it converts false to a string, it becomes "false".

var bool1:Boolean = Boolean(false);

// converts it to the number 0
trace(1 + bool1); // outputs 1

// converts it to a string
trace("String: " + bool1); // outputs String: false

Infinity Constant

See also
    Number.POSITIVE_INFINITY

-Infinity Constant

See also
    Number.NEGATIVE_INFINITY

NaN Constant

See also
    isNaN(), Number.NaN

newline Constant

var myName:String = "Lisa", myAge:Number = 30;
trace(myName+myAge);
trace("-----");
trace(myName+newline+myAge);
// output:
Lisa30
-----
Lisa
30

See also
    trace()

null Constant

A special value that can be assigned to variables or returned by a function if no data was provided. You can use null to represent values that are missing or that do not have a defined data type.

var testArray:Array = new Array();
testArray[0] = "fee";
testArray[1] = "fi";
testArray[4] = "foo";

for (i = 0; i < 6; i++) {
    if (testArray[i] == null) {
        trace("testArray[" + i + "] == null");
    }
}

The output is the following:

testArray[2] == null
testArray[3] == null
testArray[5] == null

true Constant

var shouldExecute:Boolean;
// ...
// code that sets shouldExecute to either true or false goes here
// shouldExecute is set to true for this example:

shouldExecute = true;

if (shouldExecute == true) {
    trace("your statements here");
}

// true is also implied, so the if statement could also be written:
// if (shouldExecute) {
//         trace("your statements here");
// }

var myNum:Number;
myNum = 1 + true;
trace(myNum); // output: 2

See also
    false constant, Boolean class

undefined Constant

In files published for Flash Player 6 or earlier, the value of String(undefined) is "" (an empty string). In files published for Flash Player 7 or later, the value of String(undefined) is "undefined" (undefined is converted to a string).

In files published for Flash Player 6 or earlier, the value of Number(undefined) is 0. In files published for Flash Player 7 or later, the value of Number(undefined) is NaN.

The value of undefined.toString() is undefined.

The value undefined is similar to the special value null. When null and undefined are compared with the equality (==) operator, they compare as equal. However, when null and undefined are compared with the strict equality (===) operator, they compare as not equal.

In the following example, the variable x has not been declared and therefore has the value undefined.

In the first section of code, the equality operator (==) compares the value of x to the value undefined, and the appropriate result is sent to the Output panel. In the first section of code, the equality operator (==) compares the value of x to the value undefined, and the appropriate result is sent to the log file.

In the second section of code, the equality (==) operator compares the values null and undefined.

// x has not been declared
trace("The value of x is "+x);

if (x == undefined) {
    trace("x is undefined");
} else {
    trace("x is not undefined");
}

trace("typeof (x) is "+typeof (x));

if (null == undefined) {
    trace("null and undefined are equal");
} else {
    trace("null and undefined are not equal");
}

The value of x is undefined
x is undefined
typeof (x) is undefined
null and undefined are equal