aonsager's solution

The general strategy is for each elevator to keep moving up and down, and to pick up any people along the way.

{
    init: function(elevators, floors) {
        var downQueue = [];
        var upQueue = [];
        var idleElevators = []
        var topFloor = floors.length - 1;

        _.each(elevators, function(elevator) {

            elevator.on("idle", function() {
                // record that this elevator is idle, so it can be woken up later
                idleElevators.push(elevator);
            });

            elevator.on("floor_button_pressed", function(floorNum) {
                // add the new floor to the queue if it wasn't already requested
                if (elevator.destinationQueue.indexOf(floorNum) < 0 ) {
                    elevator.destinationQueue.push(floorNum);
                    // sort to make sure we visit floors in order
                    elevator.destinationQueue = elevator.destinationQueue.sort();
                    if (elevator.goingDownIndicator()) { 
                        elevator.destinationQueue = elevator.destinationQueue.reverse();
                    }
                    // apply the changes
                    elevator.checkDestinationQueue();
                }
            });

            elevator.on("stopped_at_floor", function(floorNum) {
                if (floorNum == 0) {
                    // start moving up once we reach the bottom
                    elevator.goingDownIndicator(false);
                    elevator.goingUpIndicator(true);
                } else if (floorNum == topFloor) {
                    // start moving down once we reach the top
                    elevator.goingUpIndicator(false);
                    elevator.goingDownIndicator(true);
                }
            });

            elevator.on("passing_floor", function(floorNum, direction) {
                // check if there is someone here who wants to go our direction
                queue = direction == "up" ? upQueue : downQueue;
                index = queue.indexOf(floorNum);
                if ( index >= 0) {
                    // if yes, remove them from the queue and stop for them
                    queue.splice(index, 1);
                    elevator.goToFloor(floorNum, true);
                } else {
                }
            });
        });

        _.each(floors, function(floor) {

            floor.on("up_button_pressed", function() {
                // if there is an idle elevator, wake it up
                if (idleElevators.length > 0) {
                    elevator = idleElevators.shift();
                    elevator.goToFloor(floor.floorNum());
                } else {
                    // otherwise add this floor to the queue and wait for an elevator to pass
                    if (upQueue.indexOf(floor.floorNum()) < 0) upQueue.push(floor.floorNum());
                }
            });

            floor.on("down_button_pressed", function() {
                // if there is an idle elevator, wake it up
                if (idleElevators.length > 0) {
                    elevator = idleElevators.shift();
                    elevator.goToFloor(floor.floorNum());
                } else {
                    // otherwise add it to the queue and wait for an elevator to pass
                    if (downQueue.indexOf(floor.floorNum()) < 0) downQueue.push(floor.floorNum());
                }
            });
        });


    },
    update: function(dt, elevators, floors) {
        // We normally don't need to do anything here
    }
}