lib/rotjs-library/manual/pages/scheduler.html

<h2>Turn scheduling</h2>

<p>In turn-based games, <em>actors</em> (player, enemies, everything that moves or acts) often differ by their speed. However, since the game happens in turns, 
the speed is more accurately described as a frequency in which turns happen for a particular actor. <code>ROT.Scheduler</code> is a simple tool designed to 
simplify the task of selecting proper actor for a turn, based on the abstract speed of all actors.</p>

<p>First, you need to fill the scheduler instance with actors. There are very few requirements on actors: they need to be JS objects with method <code>getSpeed()</code>, 
which returns a number. An actor with speed=100 will get twice as many turns as actor with speed=50.<br/>
You can then repeatedly call the scheduler's <code>next()</code> method: it returns the actor whose turn should start.</p>

<div class="example">
var scheduler = new ROT.Scheduler();
var getSpeed = function() {
	return this.speed;
}

/* generate four actors */
for (var i=0;i&lt;4;i++) {
	var actor = {
		speed: ROT.RNG.getPercentage(),
		number: i+1,
		getSpeed: getSpeed
	}
	scheduler.add(actor);
	SHOW("Object #%s has speed %s.".format(actor.number, actor.speed));
}

/* simulate several turns */
var turns = [];
for (var i=0;i&lt;40;i++) {
	var next = scheduler.next();
	turns.push(next.number);
}

SHOW("\nGenerated order of turns:");
SHOW(turns.join(" ") + " ...");
</div>