This is a nice logic challenge and a javascript training tool http://play.elevatorsaga.com/

elevatorsaga.js

{
  Elevator: function(elevator) {
    this.bindEvents = function() {
      elevator.on("idle", function() {
        elevator.goToFloor(0);
      });
      elevator.on("floor_button_pressed", function(floorNum) {
        elevator.goToFloor(floorNum);
      });
    };

    this.goToFloor = function(floorNum) {
      elevator.destinationQueue.push(floorNum);
      elevator.checkDestinationQueue();
    };

    this.score = function() {
      return 1 / elevator.destinationQueue.length;
    };
  },

  Elevators: function(elevators) {
    this.bestOne = function(floorNum) {
      var index = 0;
      var score = 0;
      elevators.forEach(function(elevator, i) {
        if(score < elevator.score()) {
          index = i;
          score = elevator.score();
        }
      });
      return elevators[index];
    };
  },

  Floor: function(floor, elevators) {
    this.bindEvents = function() {
      floor.on("up_button_pressed", function() {
        elevators.bestOne(this.floorNum()).goToFloor(this.floorNum());
      });
      floor.on("down_button_pressed", function() {
        elevators.bestOne(this.floorNum()).goToFloor(this.floorNum());
      });
    };
  },

  Floors: function(floors) {
  },

  init: function(elevators, floors) {
    var self = this;

    elevators = elevators.map(function(elevator) { return new self.Elevator(elevator); });
    elevators.forEach(function(elevator) { elevator.bindEvents(); });
    elevators = new this.Elevators(elevators);

    floors = floors.map(function(floor) { return new self.Floor(floor, elevators); });
    floors.forEach(function(floor) { floor.bindEvents(); });
    floors = new this.Floors(floors);
  },

  update: function(dt, elevators, floors) {
  }
}