total=items.length,
	max=total-1,
	curr=0,
	step=500,
	to,
	delay=3000,
	
	move=function(c){
		m.style.top=(-c*step)+'px';
	},
	move_n=function(e){
		if(curr<max)
			move(++curr);
		if(curr>=max)
			f=move_p;
	},
	move_p=function(e){
		if(curr>0)
			move(--curr);
		if(curr<=0)
			f=move_n;
	},
	go=function(e){
		to=W.setTimeout(f,delay);
	},
	f=move_n;
	
	m.addEventListener('transitionend',go);

	go();

<script>
function foo(a) {
    var b = Array(a + 1).join("1").split("").map(function(b, a) {
            return a + 1
        }),
        b = b.concat(b.slice(1, a - 1).reverse());
    return function() {
        var a = b.shift();
        b.push(a);
        return a
    }
};
var x = foo(5)
for (var i=0; i<50; i++)  {document.write(x()+ ' ')}
</script>

<script>
function foo(c) {
    var a = 2,
        b = !1;
    return function() {
        b ? a++ : a--;
        if (a == c || 1 == a) b = !b;
        return a
    }
};
var x = foo(5)
for (var i=0; i<50; i++)  {document.write(x()+ ' ')}
</script>

<script>
var a = [0, 1, 2, 3, 4, 5];
function sdir(d) {
    d==1 ? a.unshift(a.pop()) :  a.push(a.shift());
    document.getElementById('s').innerHTML = a.join(', ');
}
</script>
<button onclick="sdir(1)">&laquo;</button> <button onclick="sdir(-1)">&raquo;</button>
<div id="s">0, 1, 2, 3, 4, 5</div>

go_to=function(e){
		if(e.target.nodeName='I'){
			curr=parseInt(e.target.getAttribute('data-index'));
			if(f===move_p)
				++curr;
			else
				--curr;
			f();
		}
	};

v={o:5};

parseInt(('n' in v));
/*
NaN
*/

abs=function(el){
		var v = atv(el);
		if(v)
			return v.replace('-','');
	},

<style>
input {
  float: left;
  width:120px;
}
#result {
  width: 240px;
  height: 90px;
  background-color: red;
  color: #fff;
  font-size: 80px;
  text-align: center;
}
#buttons {
  width:240px;
}
</style>
<div id="result"></div>
<div id="buttons">
    <input type="button" value="Previous" id="prev" />
      <input type="button" value="Next" id="next" />
      <input type="button" value="Play" id="play" />
      <input type="button" value="Pause" id="pause" />
</div>
<script>
function nav(max) {
  this.max = max;
  this.current = this.current || -1;
  this.next = function () {
    this.current = this.current < this.max - 1 ? this.current + 1 : 0;
    return this.current;
  };
  this.prev = function () {
    this.current = this.current > 0 ? this.current - 1 : this.max - 1;
    return this.current;
  };
};
 
var animTimer, slider = new nav(8);
function sliderPlay() {
  animTimer = setInterval(function () {
    result.innerHTML = slider.next();
  }, 1000);
};
next.onclick = function () {
  result.innerHTML = slider.next();
};
prev.onclick = function () {
  result.innerHTML = slider.prev();
};
play.onclick = function () {
  if (animTimer) return;
  sliderPlay();
};
pause.onclick = function () {
  clearInterval(animTimer);
  animTimer = 0;
};
window.onload = function () {
  sliderPlay();
};
</script>

var obj = {
    min: 0,
    max: 0,
    __reverce: 1,
    __position: 0,
    get cur() {
        this.__position += this.__reverce
        if (this.__position == this.max || this.__position == this.min) this.__reverce *= -1;
        return this.__position;

    },
    set cur(arg) {
        this.__position = arg;
    }
};
obj.max = 10, obj.cur = 8;
console.log(obj.cur);
console.log(obj.cur);
console.log(obj.cur);

var curr=0, max=5,i=-1;

function next(){

  if(curr==max || curr==0)
    i=-i;

  curr+=i;
  
  console.log( curr);

}

for(var j=0;j<20;j++)
  next();

/* calc curr and move block */
	move=function(j){
		i=j||i;
		curr+=i;

		if(curr==max || curr==0)
			i=-i;

		render();
		m.style.top=(curr*-step)+'px';
	},
	/* next - previous click */
	move_n=function(e){
		move(1);
	},
	move_p=function(e){
		move(-1);
	},
	/* animation */
	stop=function(e){
		if(to){
			W.clearTimeout(to);
			to=false;
		}
	},
	go=function(e){
		to=W.setTimeout(move,delay);
	},
	go_n=function(e){
		if(to!==false)
			go(e);
	},
	/* direct click */
	go_to=function(e){
		if(e.target.nodeName='I'){

			curr=parseInt(e.target.getAttribute('data-index'))-i;
			
			move();
			
			if(curr==max)
				i=-1;
			else if(curr==0)
				i=1;


		}
	};

	
	if(total>1){
		btn_n.addEventListener('click',move_n);
		btn_p.addEventListener('click',move_p);
		btn_b.addEventListener('click',go_to);
		p.addEventListener('mouseenter',stop);
		p.addEventListener('mouseleave',go);
		m.addEventListener('transitionend',go_n);
		W.addEventListener('focus',go);
		W.addEventListener('blur',stop);
	}