Fix the postion of vote buttons when scrolling

fixedVoteButton.js

// run this in a question page
// just a demo, compatibility hasn't been tested
(function(){
	// utility
	function s(syntax){
		// a simple selector, support ID, Class and tag.
		if(syntax&&typeof(syntax)==="string"){
			if(/^#/.test(syntax)){
				return document.getElementById(syntax.slice(1));
			}else if(/^\./.test(syntax)){
				return document.getElementsByClassName(syntax.slice(1));
			}else{
				if(document.getElementsByTagName(syntax).length<1){
					if(document.getElementById(syntax)===null){
						return document.getElementsByClassName(syntax);
					}else{
						return document.getElementById(syntax);
					}
				}else{
					return document.getElementsByTagName(syntax);
				}
			}
		}else{
			return undefined;
		}
	}
	function findTop(obj) {
		// find the top offset of an element
		var curtop = obj.offsetTop;
		while (obj.offsetParent !== null) { 
			curtop += obj.offsetParent.offsetTop;
			obj = obj.offsetParent;
		}
		return curtop;
	}
	
	// detect vote postion and change it
	function detect(element){
		// detect and alter the position of vote buttons
		var screenToTop = document.body.scrollTop || document.documentElement.scrollTop, // distance from window top to page top
				eTop = findTop(element), // element top to window 
				vote = element.childNodes[1], //vote element
				voteHeight = 44; //button height
				abLeft = element.offsetLeft-30+"px"; // button left to window left
		if(screenToTop - eTop>=-4 && screenToTop-eTop-element.offsetHeight < -206){
			// just fixed vote		
			if(!(/\bfixedVote\b/.test(vote.className))){
				vote.className += " fixedVote";
			}
			vote.setAttribute('style','position:fixed;top: 4px;left: '+ abLeft);
		}else if(screenToTop - eTop>=-4 && screenToTop-eTop-element.offsetHeight < -161){
			// when vote button is about to vanish, gradually alter its position
			if(!(/\bfixedVote\b/.test(vote.className))){
				vote.className += " fixedVote";
			}
			var t_t = (-206-(screenToTop-eTop-element.offsetHeight))+ "px;";
			vote.setAttribute('style','position:fixed;top: '+t_t+ 'left: '+ abLeft);
		}else{
			// return to original state
			if(/\bfixedVote\b/.test(vote.className)){
				vote.className = vote.className.slice(0,-10);
				vote.setAttribute('style','position:absolute;left: -30px');	
			}
		}
	}
	function onPageScroll(e){
		// page scroll event
		var ans = s('xyr');
		for(var i=0;i<ans.length;i++){
			if(s('xyr')[i].offsetHeight > 300){
				detect(s('xyr')[i]);
			}
		}
	}
	
	window.addEventListener('scroll', onPageScroll, false);
	//console.log(s('xnq')); //vote
	//console.log(s('xyr')); //doc
})();