fnObj = window[functionName] is not a function issue - eval() works well

Question

I'm just overworking my JS code and wish to replace my eval()'s with window[functionName]. So I just made a quick test in the JSFiddle and all works well with the following lines:

var fnName = "Page_test";
var foo = "yammy";
var Page_test = function(bar) {
    return bar;
}
var Obj = window[fnName];
alert(Obj(foo));

(Link to this JSFiddle -> http://jsfiddle.net/juSHj/)

Now I try to replace the following lines of code with the evil eval() with the above concept:

old code: (works like a charm / fired after ajax success)

 ...
 success: function(ret) {
     if(returnFnAjaxForm != "") {
          eval(returnFnAjaxForm+"('"+encodeURI(jQuery.trim(ret))+"')");
     }
 }
 ...

new code:

Returns: Uncaught TypeError: Property 'dummyFn' of object [object Window] is not a function

...
success: function(ret) {
     if(returnFnAjaxForm != "") {
          fnObj = window[returnFnAjaxForm];
          if(typeof(fnObj) == "function") { // this is optional
               fnObj(encodeURI(jQuery.trim(ret)));
          }
     }
} 
...

I'm curious where I made my mistake. Yes the function I try to fire exists and is defined with var . Is this concept may not possible to use it on an ajax-response?

Thanks for any help.

(Using jQuery)

Answer 1

If you declare your function in a closure, it's not a member of window. Example :

var in_window = '132';
alert(window['in_window']); // Alert 132

(function() {
    var not_in_window = '132';
    alert(window['not_in_window']); // Alert undefined
})();

So be careful of where you declare your Page_test variable. If you really want to put in window, you can do window.Page_test = Page_test.

The best you can do is to use an object for all your possible callbacks. Like this :

var callbacks = {
    foo : function() {},
    foo1 : function() {},
    foo2 : function() {},
    foo3 : function() {}
};

var obj = callbacks[fnName];