Is it possible to get the name of an anonymous JavaScript function?

Question

Is it possible to get the name of an anonymous function that declared as follows?

var F = function(){};

At first sight, the answer is no, but apparently the browsers know and hold the function name:

var F = function(){};
var x = new F();
console.log(x.constructor);   // function F()

(Firefox)

var F = function(){};
var x = new F();
console.log(x);    // F {}

(Chrome)

Is this name somehow accessible? I need it mainly for error logging, so the solution doesn't have to be cross-browser.

Edit for clarification:

I'm getting an objects from external code that I need to know their types, therefore obvious answers like using another declaration ways are not what I'm searching.

Answer 1

In the use-case that you're trying, it's possible that there can be more than one variable holding the same anonymous function.

ie, it can go on like:

var F = function(){};
var x = new F();
var x2 = x;
var x3 = x;
var blah = x3;

So, now we have more than one name to look for. And the first thing I thought of is to loop through all the objects under window and print their name which is having the same method as the value.

So, you'd think of something like:

for each (item in window){
   if (myfunc == item){
      console.log(/*Somehow print the actual name of the item */)
   }
}

But, it doesn't work that way since, now item is another variable, and look like there is no built-in property that gives the variable name. May be, have a look at Variable name as a string in Javascript , not that it helps here, though...

So, finally, since you mentioned you're trying to do error logging, thought of using stack-traces. Don't know if it will apply in your situation, may be still a bit enlightening :)

And this is how it goes: (To be warned, this is a hack)

var myFunction = function(){   
  var err = new Error();   
  console.log(err.stack) 
} 
myFunction();

will output something like:

myFunction@debugger eval code:3:17
@debugger eval code:6:5
@debugger eval code:1:15

And, taking that to the next level:

var myFunction = function(){   
  var err = new Error();   
  console.log(err.stack.split("@")[0]) 
 /* split the stack-trace string and get the first word before @ */
} 
myFunction();

Now, the output for that will be:

myFunction

Which, indeed is the name of the variable that is holding the anonymous function.

Note: This answer is inspired by the question How can I get a Javascript stack trace when I throw an exception?

Have tried this only in Firefox, there's a chance the stack-trace might be different elsewhere.

Edit: Failed to notice your edit, this might need editing of declarations, which breaks your use-case. :(