Create anonymous methods using "eval" - browser behavior

Question

I am working with jQuery and I need to create an anonymous method with the eval () function.

The following lines worked with Opera, but not with IE, FF, Chrome:

var callbackStr = "function(){alert('asdf');}";  
var callback = eval(callbackStr);  
callback();

This code works with all browsers:

var callbackStr = "var callback = function(){alert('asdf');}";  
eval(callbackStr);  
callback();  

You see, I have already solved my problem. But I want to know what exactly is happening. Can someone explain this behavior to me or let me know where I can find additional information?

(PS: I know this page .)

Answer 1

, , JSON, eval - eval treats { , eval - FunctionDeclaration. eval , , :

var callbackStr = "(function(){alert('asdf');})";  
var callback = eval(callbackStr);  
callback();
// -> alerts 'asdf';

, Opera - , . eval, , ( ).

, 12.4 ECMA-262 3rd Edition:

, ExpressionStatement , . , ExpressionStatement function, FunctionDeclaration.

.

Answer 2

, eval

var callbackStr = "function(){alert('asdf');}";  
var callback = eval("(" + callbackStr + ")");  
callback();

Answer 3

eval ​​. , - var callback .

, , eval , .

Answer 4

. , , .