Scrollwatcher - simple waypoint -requires jQuery and mousewheel plugin

scrollwatcher.js

function ScrollWatcher(){
	this.watchers = [];
	this.lastY = 0;
	this.first = true;

	var scroll = function(event){
		var y = window.pageYOffset,
			self = this,
			diff = y - this.lastY,
			dir =  diff >= 0 ? 'down' : 'up';

		this.lastY = y;

		$.each(this.watchers, function(i, watcher){
			if(watcher.y < y ){
				if(watcher.called < watcher.ticks ){
					/*
						if its the first scroll an we are allready over the watchers y
						we call each fn
					*/
					if(self.first){
						$.each(watcher.fns, function(i, fn){
							fn.call(self, event, y, dir);
						});
						watcher.called = watcher.ticks; 
						return;
					};

					var fn = watcher.fns[watcher.called];
					if(fn){
						fn.call(self, event, y, dir);
					}
					watcher.called++;
					event && event.preventDefault();
				} 
			} 
		});

		if(this.first){
			this.first = false;
		}
	};

	$(document.body).on("mousewheel", $.proxy(scroll, this));
};

ScrollWatcher.prototype = {
	constructor : ScrollWatcher,
	waypoint : function(start, ticks, fns){
		this.watchers.push({
			y : start,
			ticks : ticks, 
			called : 0,
			fns:  fns
		});
	}
};

usage.js

var watcher = new Scrollwatcher();

watcher.waypoint(200, 8, {
	6 : function(){
		$('[data-waypoint="4"]').addClass("active");
	},
	4 : function(){					
		$('[data-waypoint="3"]').addClass("active");
	}, 
	2 : function(){					
		$('[data-waypoint="2"]').addClass("active");
	} 
});