It's not a double callback, it's just a test to see if the callback
function exists before calling it.
Javascript only evaluates the expressions necessary to determine whether
a logical expression is true or false. So if I write
(1==2 && foo())
Javascript notices that 1==2 is false, and knows that (False && True)
and (False && False) are both False. So it doesn't need to evaluate
foo() in order to determine that the whole expression is False, and it
doesn't call foo().
In the case of
_xdc_._1fsm2u0k2 && _xdc_._1fsm2u0k2(...)
if _xdc_._1fsm2u0k2 is undefined or void or null, then Javascript
doesn't need to evaluate _xdc_._1fsm2u0k2(...) to determine that the
whole expression is false.
On the other hand, if _xdc_._1fsm2u0k2 is a real function reference, in
boolean context that's considered True, so Javascript has to evaluate
the rest of the logical expression in order to determine if the entire
expression is True or False.
--
http://econym.org.uk/gmap
The Blackpool Community Church Javascript Team
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