Undefined - MACROMEDIA FLASH MX 2004-ACTIONSCRIPT LANGUAGE Reference

undefined

Availability
Flash Player 5.
Usage
undefined
Parameters
None.
Returns
Nothing.
Description
A special value, usually used to indicate that a variable has not yet been assigned a value.
A reference to an undefined value returns the special value
typeof(undefined)
is .
undefined
In files published for Flash Player 6 or earlier, the value of
"" (an empty string). In files published for Flash Player 7 or later, the value of
undefined.toString()
The value
undefined
compared with the equality (
are compared with the strict equality (
undefined
Example
In the following example, the variable
. In the first section of code, the equality operator (
undefined
value
undefined
code, the equality (
// 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");
}
returns the string
is
undefined
is similar to the special value
) operator, they compare as equal. However, when
==
x
, and the appropriate result is sent to the Output panel.In the second section of
) operator compares the values
==
ActionScript Language Reference
undefined
. The only value of type
"undefined"
undefined.toString()
.
. When
null
) operator, they compare as not equal.
===
has not been declared and therefore has the value
and
null
CHAPTER 2
. The ActionScript code
undefined
is
and
null undefined
null
) compares the value of
==
.
undefined
undefined
are
and
to the
x
989