overwrite mongodb document

db.js

DB.prototype.updateTodo = function(id, val, fn) {
	this.db.collection('todo').update({ _id : id }, val, function(err) {
		if (err) return fn(err);
		console.log(arguments);
		fn(null);
	});
};


/*
console.log output:
  { '0': null,
  '1': 0,
  '2': 
   { updatedExisting: false,
     n: 0,
     connectionId: 707,
     err: null,
     ok: 1 } }
*/