Accessing variables trapped by closure

Question

I was wondering if there is any way to access variables trapped by closure in a function from outside the function; e.g. if I have:

 A = function(b) {     var c = function() {//some code using b};     foo: function() {         //do things with c;     } } 

is there any way to get access to c in an instance of A. Something like:

 var a_inst = new A(123); var my_c = somejavascriptmagic(a_inst); 

Answer 1

A simple eval inside the closure scope can still access all the variables:

function Auth(username) {   var password = "trustno1";   this.getUsername = function() { return username }   this.eval = function(name) { return eval(name) } }  auth = new Auth("Mulder") auth.eval("username") // will print "Mulder" auth.eval("password") // will print "trustno1" 

But you cannot directly overwrite a method, which is accessing closure scope (like getUsername()), you need a simple eval-trick also:

auth.eval("this.getUsername = " + function() {   return "Hacked " + username; }.toSource()); auth.getUsername(); // will print "Hacked Mulder" 

Answer 2

Variables within a closure aren't directly accessible from the outside by any means. However, closures within that closure that have the variable in scope can access them, and if you make those closures accessible from the outside, it's almost as good.

Here's an example:

var A = function(b) {     var c = b + 100;     this.access_c = function(value) {         // Function sets c if value is provided, but only returns c if no value         // is provided         if(arguments.length > 0)             c = value;         return c;     };     this.twain = function() {         return 2 * c;     }; }; var a_inst = new A(123); var my_c = a_inst.access_c(); // my_c now contains 223 var my_2c = a_inst.twain(); // my_2c contains 446 a_inst.access_c(5); // c in closure is now equal to 5 var newer_2c = a_inst.twain(); // newer_2c contains 10 

Hopefully that's slightly useful to you...