请大大帮我分析一下这段javascript代码

[lau]

大大帮我看一下这段代码与图片之间的关系，谢谢

<script language="javascript">
var page = 1;
var s = location.search.substring(1,location.search.length);
if (!isNaN(s) && s != "")
{
	if (( s > 0 ) && ( s <= datas.length + 1 ))
	{
		page = s;
	}
}

function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}

function MM_showHideLayers() { //v6.0
  var i,p,v,obj,args=MM_showHideLayers.arguments;
  for (i=0; i<(args.length-2); i+=3) if ((obj=MM_findObj(args[i]))!=null) { v=args [i+2];
    if (obj.style) { obj=obj.style; v=(v=='show')?'block':(v=='hide')?'none':v; }
    obj.display=v; }
}

function foo(o)
{
	var v = parseInt(o.width);
	if (v > 720)
	{
		document.all.it1.width = v;
		document.all.it2.width = v+70
	}
	MM_showHideLayers('Layer2','','hide');
	tmp=0;
}

function showpic(v)
{
	var nl = new String(window.location);
	if (nl.indexOf("?") >-1)
	{
		nl = nl.substring(0,nl.indexOf("?"));
	}
	nl = nl+'?'+v;
	//alert (nl);
	window.location = nl;
}

function ch_sel(v)
{
	document.all.select1.value = v;
	document.all.select2.value = v;
}

function get_sel(v)
{
	if (v == 0)
	{
		//document.write
		var i,outstr = "";
		for (i=1;i<datas.length;i++)
		{
			outstr += "<option value='"+ i +"'>第"+ i +"页</option>";
		}
		document.write(outstr);
	}
	else
	{
		if ((v > 0) && (v < datas.length+1))
		{
			page = v;
			showpic(v);
			ch_sel(v);
		}
	}
}

function prevpage()
{
	page--;
	if (page <1)
	{
		alert('到头咧');
		page = 1;
	}
	else
	{
		//alert(page);
		ch_sel(page);
		showpic(page);
	}
}

function nextpage()
{
	page++;
	//alert (page);
	if (page >= datas.length )
	{
		alert('到头咧');
		page = datas.length-1;
	}
	else
	{
		//alert(page);
		ch_sel(page);
		showpic(page);
	}
}

function keylock()
{
	if((event.keyCode == 78 || event.keyCode == 110) && (event.ctrlKey))
	{
		event.returnValue = false;
	}
	if((event.keyCode == 121) && (event.shiftKey))
	{
		event.returnValue = false;
	}
}

function keyUp()
{
	if (window.event.keyCode == 93)
	{
		addFavorite();
	}
	if (window.event.keyCode == 17)
	{
		if (tmp == 1)
		document.getElementById("next").click();
		tmp = 1;
	}
	if (window.event.keyCode == 16)
	{
		if (tmp == 3)
		document.getElementById("prev").click();
		tmp = 3;
	}
}

</script>