Access local variable inside a callback function

Question

var inner = function() { console.log(x); }

// test 1
(function(cb) { var x = 123; cb(); })(inner);

// test 2
(function(cb) { var x = 123; cb.apply(this); })(inner);

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Answer 1

The only way to access the local variable x in the callback, is to pass it as an argument:

var inner = function(some_var) { console.log(some_var); }; //logs 123
(function(cb) { var x = 123; cb(x); })(inner);

OR

var inner = function(some_var) { console.log(some_var); }; //logs 123
(function(cb) { var x = 123; cb.apply(this,[x]); })(inner);

OR

var inner = function(some_var) { console.log(some_var); }; //logs 123
(function(cb) { var x = 123; cb.call(this,x); })(inner);

FURTHER

Because JS is lexically scoped, trying to reference the local variable after the anonymous function has finished executing is impossible by any other means. If you don't pass it as an argument to make it available elsewhere, JS will see it as non-reachable and it will be eligible for garbage collection.