MACROMEDIA FLASH MX, Справочник

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1004 Chapter 2: ActionScript Language Reference
void
Availability
Flash Player 5.
Usage
void ( expression )
function functionName ():Void {}
Description
Usage 1: Operator; a unary operator that discards the
expression
value and returns an undefined
value. The
void
operator is often used in comparisons using the equality (
==
) operator to test for
undefined values.
Usage 2: Data type; used in function definitions to indicate that a function will not return a value.
Example
Usage 1: In the following ActionScript, the
void
operator is used to test for undefined values:
if (someUndefinedVariable == void (0)) {
trace("someUndefinedVariable is undefined");
}
The previous code can also be written in the following way:
if (someUndefinedVariable == undefined) {
trace("someUndefinedVariable is undefined");
}
Usage 2: In the following example, a function that returns a value is defined using the
Void
return
type, which results in a compile-time error:
function myFunction():Void {
return "This will cause a compile-time error.";
}
/* the following function call will generate a compile-time error:
**Error** Scene=Scene 1, layer=Layer 1, frame=1:Line 2: A function with return
type Void may not return a value.
return "This will cause a compile-time error.";
*/
myFunction();
CHAPTER 2
ActionScript Language Reference