gistfile1.js

function join(f1, f2) {
      return function (callback) {
             var doneOnce = false;
	     f1(function () { 
			if (doneOnce) 
		 	{ 
				callback(); 
			} 
			doneOnce = true;});
             f2(function () { 
			if (doneOnce) 
			{ 
				callback(); 
			} 
			doneOnce = true;});
      }
}