gistfile1.js

// add a log() method to all function objects
Function.prototype.log = function() {
  var __method = this;

  return function() {
    var name = /function\s*(.*)\s*\(/.exec( __method );
    console.log( "called " + ( name[1] || "[unknown]" ) + "()", arguments );
    return __method.apply( null, arguments );
  }
}

// declare some function as normal
function foo() {
  console.log( "I'm foo!" );
  return true;
}

// call the function, no logging by default. output:
//    I'm foo!
foo( { x: 'yz' } );

// turn logging on
foo = foo.log();

// calls are now logged to the console. output:
//    called foo() [Object x=yz]
//    I'm foo!
foo( { x: 'yz' } );

// alternatively, you could have turned it on when it was declared
/*
var foo = (function foo() {
  console.log( "I'm foo!" );
  return true;
}).log();
*/

// works for anonymous functions too, but output is a little different. output:
//    called [unknown]() [Object x=yz]
//    I'm anonymous
(function() {
  console.log( "I'm anonymous" );
}).log()( { x: 'yz' } );