Question

Does the placement of a function have an effect on the performance of closures within scope? If so, where is the optimal place to put these functions? If not, is the implied association by closure enough reason to place a function in another place logically?

For instance, if foo does not rely on the value of localState, does the fact that localState is accessible from foo have implications as to foo‘s execution time, memory use, etc.?

(function(){     var localState;      function foo(){         // code     }      function bar(){         // code         return localState;     } })(); 

In other words, would this be a better choice, and if so why?

(function(){     function foo(){         // code     }      var localState;      function bar(){         // code         return localState;     } })(); 

Darius Bacon has suggested below that the two samples above are identical since localState can be accessed anywhere from within the block. However, the example below where foo is defined outside the block may be a different case. What do you think?

function foo(){     // code }  (function(){      var localState;      function bar(){         // code         foo();         return localState;     } })(); 

Answer 1

Every function in Javascript is a closure. The runtime to resolve a variable’s value is only incurred if the variable is referenced by the function. For instance, in this example function y captures the value of x even though x is not referenced directly by y:

var x = 3; function y() eval('x'); y(); 3