[iNils]

function ABC () {
	this.link = 0;
	this.array = [1, 0, 0];
}
ABC.prototype.setOn = function (val) {
	val = Math.floor (val)
	if (val < this.array.length && val >= 0) {
		this.array[this.link] = 0;
		this.link = val;
		this.array[val] = 1;
	}
	return this;
};
ABC.prototype.toString = function () {
	return this.array.join ("");
};
abc = new ABC ();
trace (abc);
trace (abc.setOn (0));
trace (abc.setOn (1));
trace (abc.setOn (2));
trace (abc.setOn (3));
trace (abc.setOn (0));