Helper function for Bit's Quest (bitsquest.bitbucket.org) that launches callbacks in a sequence

bitsquest-bounce.js

var phase = 0;

var bounce = (function () {
  var nextPhaseToAssign = 0;
  var opposite = {
    top: 'bottom',
    left: 'right',
    bottom: 'top',
    right: 'left'
  };
  return function assign(direction) {
    if (!direction) {
      return;
    }
    var customHandler;
    if (Array.isArray(direction)) {
      customHandler = direction[1];
      direction = direction[0];
    }
    var myPhase = nextPhaseToAssign++;
    this.on('sensor:' + direction, function (contact) {
      if (contact && phase == myPhase) {
        if (customHandler) {
          customHandler.call(this);
        }
        else {
          // Default handler.
          this.thrusters[opposite[direction]](false);
          this.thrusters[direction](true);
        }
        phase += 1;
      }
    });
    assign.apply(this, [].slice.call(arguments, 1));
  }.bind(this);
}.call(this));

// Example: solution for #5 "Going Up"
// http://bitsquest.bitbucket.org/index.html#5

this.on('start', function () {
  this.thrusters.left(true);
  this.thrusters.top(true);
});

bounce('bottom',
       'right',
       'top',
       'left',
       'bottom',
       'right',
       'top',
       ['bottom', function () {
         this.thrusters.right(false);
         this.thrusters.top(false);
         this.thrusters.left(true);
         this.thrusters.bottom(true);
       }]
      );