could this be done without making a copy of the entire object in the update method?

update_state.js

var Stateful = function(states, init_state) {
  if (typeof(states) === 'number') {
    this.states = [];
    for (var i = 0; i < states; i++) {
      this.states[i] = "_" + i; //prefix with _ (_0,_1,_2...) so state labels are strings 
    }
  } else {
    this.states = states;
  }
  this.state = this.states[init_state];
  this.last = this.state;
}

Stateful.prototype = {
  get: function() {
    return this.state;
  },
  update: function (new_state,delay) {
    var self = this; //looking for a better way to do this
    delay = (typeof(delay) === 'number') ? delay : 0;
    if (delay === 0) {
        this.last = this.state;
        this.state = new_state;
    } else {
      window.setTimeout(function() {
        self.update(new_state);
      }, delay);
    }
  }
};