6.js

/*
 * The round switches won't stay on unless something is placed on top of them.
 */

var robot = this;
var thrusters = ['left', 'top', 'right', 'bottom'];
var state = 0;
var start = 'top';
var rules = [/* 0 */ [['bottom', 'left', 0],
					  ['right', 'bottom', 0],
					  ['left', 'right', 1]],
             /* 1 */ [['left', 'bottom', 2]],
             /* 2 */ [['top', 'left', 2],
                      ['right', 'top', 2],
					  ['left', ['left', 'bottom'], 3]],
             /* 3 */ [['top', 'left', 3]]];
function fire(thruster) {
	robot.thrusters[thruster](true);
}
function multiFire(thrusters) {
	if(Array.isArray(thrusters)){
		for(var i=0; i<thrusters.length; i++){
			var thruster = thrusters[i];
			fire(thruster);
		}
	}else{
		fire(thrusters);
	}
	
}
function stopAll() {
	for(var i=0; i<thrusters.length; i++){
		robot.thrusters[thrusters[i]](false);
	}
}

function getState() {
	return state;
}
function setState(next) {
    console.log(state + " -> " + next);
	state = next;
}

function searchSensor(sensor, rules) {
	for(var i=0; i<rules.length; i++){
		var rule = rules[i];
		var curSensor = rule[0];
		if(sensor == curSensor)
			return [rule[1], rule[2]];
	}
	return null;
}

robot.on('start', function() {
	multiFire(start);
});

for(var i=0; i<thrusters.length; i++){
	var s = thrusters[i];
	(function(){
        var sensor = s;
		robot.on('sensor:'+sensor, function(contact) {
			if(contact){
				var next = searchSensor(sensor, rules[getState()]);
				if(next != null){
                    console.log("sensor: " + sensor);
					var nextThruster = next[0];
					var nextState = next[1];
					stopAll();
					multiFire(nextThruster);
					setState(nextState);
				}
			}
		});
	})();
}

solution for level 6 of Bitbucket Bit's Quest
see discussion on juick.com