[ruslan_mart]

var a = function(arg)
{
   if(this.a) return new a(arg);
   if(arg)
   {
      this.arg = arg;
      //code
   }
}

a.prototype = {
   fo: function(b)
   {
      alert(this.arg + b);
      return this;
   },
   gi: function(b)
   {
      alert(this.arg - b);
      return this;
   }
}

a(5).fo(4); //9
a(7).gi(3); //4

a(5).fo(4).gi(3).fo(4).gi(3).fo(4).gi(3).fo(4).gi(3).fo(4).gi(3) //....

Вот ещё, я тут на днях эксперементировал:

var $d = document;

var $E = function(a)
{
	if(this.$E) return new $E(a);
	if(typeof a == 'string')
	{
		var b = a.substr(0,1), c = a.substr(1);
		if(b == '#') this.a = $d.getElementById(c);
		else if(b == '.') this.a = $d.getElementsByClassName(c);
		else this.a = $d.getElementsByTagName(a);
	}
	else this.a = a;
}
$E.prototype = {
	append: function(a)
	{
		if(a) for(i=0; i<this.a.length; i++) this.a[i].innerHTML += a;
		return this;
	},
	attr: function(a, b)
	{
		if(a) for(i=0; i<this.a.length; i++)
		{
			if(typeof a == 'string' && b) this.a[i].setAttribute(a, b);
			if(typeof a == 'object') for(k in a) this.a[i].setAttribute(k, a[k]);
			else if(!b) return this.a[0].getAttribute(a);
		}
		return this;
	},
	delete: function()
	{
		for(i=0; i<this.a.length; i++) this.a[i].parentNode.removeChild(this.a[i]);
		return this;
	},
	fade: function(a, b, c)
	{
		if(a)
		{
			var d = this, e, f;
			for(i=0; i<this.a.length; i++)
			{
				e = e = d.a[i].style;
				e.display = 'block';
				e.transition = 'opacity '+(a/1000)+'s';
				if(e.opacity != '0')
				{
					e.opacity = 0;
					f = 1;
				}
				else e.opacity = 1;
			}
			setTimeout(function()
			{
				if(f) b ? d.delete() : d.style('display', 'none');
				if(c) c(d.a);
			}, a);
		}
		return this;
	},
	html: function(a)
	{
		if(a !== undefined) for(i=0; i<this.a.length; i++) this.a[i].innerHTML = a;
		else return this.a[0].innerHTML;
		return this;
	},
	style: function(a, b)
	{
		if(a) for(i=0; i<this.a.length; i++)
		{
			if(typeof a == 'string' && b) this.a[i].style[a] = b;
			if(typeof a == 'object') for(k in a) this.a[i].style[k] = a[k];
			else if(!b) return this.a[0].style[a];
		}
		return this;
	}	
}