Comfortably Coding Blog of Mathew Rodley

Reading Steve's blog today I saw his post on accessing the current functions name in python. This could end up being a useful thing to know if you are playing with some unfamiliar code and need this sort of information, or are doing something nasty. So without anymore fuss here's how to do the same thing in Ruby and JavaScript!

JavaScript

We can access the current functions name through arguments.callee.name, in fact to take this a bit further, arguments.callee is the function actually being called (so we can recurse in anonymous functions!

function NamedFunction() { console.log(arguments.callee.name); }
var fn = NamedFunction;
fn();

Outputs: "NamedFunction"

Ruby

In Ruby you can use the caller method of the Kernel module (all objects have this). caller returns an array of strings representing the stack and we can use this (as Ruby Facets does) to find out the current functions name. Ruby Facets extend the Kernel module with `called`:

module Kernel
def called
/`([^']+)'/.match(caller(1).first)[1].to_sym
end
end

and one can now write

def namedFunction
puts called
end
namedFunction()

Outputs "namedFunction"

JavaScript Stack trace

Getting a stack trace in JavaScript is a fun task, because browsers are not the same, but here are some quick tips. When Firefox throws an exception, that exception has a 'stack' member which contains a stack trace. For example:

try { var x = nil; x.x; } catch(e) {console.log(e.stack); }

Opera's exceptions contain the 'message' member which contains stack information. And finally IE and Safari don't provide anything, but we can roll our own using arguments.callee.caller, which is as you guessed it the function which has called the current function. So we can roll our own!

function stack() {
var fn = arguments.callee;
while(fn = fn.caller) {
console.log(fn.name || "Anonymous");
}
}
function a() { stack() }
function b() { a() }
function c() { b() }
c();

Outputs: "a b c"

JavaScript & recursing anonymous functions

And just a little icing on the cake for the end of this post. Take some time and run this in a JavaScript Shell

var x = 0;
(function() {
console.log(x++);
if(x < 10) arguments.callee();
})();