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How does this structure work when the function is anonymous? 

 !function() { . . . }();
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  • returned value NOT ed, !false Commented Jan 27, 2014 at 12:56
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    Also see stackoverflow.com/questions/9091289/…, which, in turn, seems to be a triple duplicate. ) Commented Jan 27, 2014 at 12:57
  • The anonymous function is executed, but the return value is not used anywhere. Commented Jan 27, 2014 at 13:03
  • There's no test for existence. The return value is negated and discarded. Commented Jan 27, 2014 at 13:37

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With a return value.. you negate that with !

var x=!function(){return false}(); console.log(x); // true

double negation

var pizza='pizza'; var x=!!function(){return pizza}(); console.log(x); // true // returns true if pizza is defined, not 'pizza' // returns false if pizza is ''.

demo

http://jsfiddle.net/9shzF/1/

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Pretty much as with any other thing. The anonymous function is autoexecuted, therefore returns a value, and the value is negated.

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