User Guide

126 Chapter 2: ActionScript Language Reference
Boolean()
Availability
Flash Player 5; behavior changed in Flash Player 7.
Usage
Boolean(expression) : Boolean
Parameters
expression
An expression to convert to a Boolean value.
Returns
A Boolean value.
Description
Function; converts the parameter expression to a Boolean value and returns a value as described
in the following list:
• If expression is a Boolean value, the return value is expression.
• If expression is a number, the return value is true if the number is not zero; otherwise the
return value is
false.
If
expression is a string, the return value is as follows:
• In files published for Flash Player 6 or earlier, the string is first converted to a number; the
value is
true if the number is not zero, false otherwise.
• In files published for Flash Player 7 or later, the result is true if the string has a length greater
than zero; the value is
false for an empty string.
• If expression is undefined or NaN (not a number), the return value is false.
• If expression is a movie clip or an object, the return value is true.
Note: Unlike the Boolean class constructor, the Boolean() function does not use the keyword new.
Moreover, the Boolean class constructor initializes a Boolean object to false if no parameter is
specified, while the Boolean() function returns undefined if no parameter is specified.
Example
In the following example, expressions are converted from numeric to Boolean values:
trace(Boolean(-1)); // output: true
trace(Boolean(0)); // output: false
trace(Boolean(1)); // output: true
trace(Boolean(true)); // output: true
trace(Boolean(false)); // output: false
trace(Boolean("true")); // output: true
trace(Boolean("false")); // output: true
trace(Boolean("Craiggers")); // output: true
trace(Boolean("")); // output: false
CHAPTER 2
ActionScript Language Reference