要素が見えたらアクションする

/**
 * 要素が見えたらアクションする
 *
<script>
var inview = [
	{
		'id':'newstitle'
		,'offset':300
		,'init':function(){document.getElementById('newstitle').style.marginLeft='150px';}
		,'action':function(){document.getElementById('newstitle').style.marginLeft='0px';}
	}
];
</script>
<script src="js/inview.js"></script>
 *
 * @author ao-system
 */
(function(window,document,inview){
	init();
	function init() {
		for (var i = 0; i < inview.length; i++) {
			(function(i){
				var elmY = offsettop(document.getElementById(inview[i].id)) + inview[i].offset;
				inview[i].elmY = elmY;		//反応開始位置
				var scrollY = scrolltop();
				if (elmY <= (scrollY + document.documentElement.clientHeight)) {
					inview[i].rendered = true;	//既に見えているので処理済み
				} else {
					(inview[i].init)();
					inview[i].rendered = false;	//処理済みか否か
				}
			})(i);
		}
		document.addEventListener('scroll',function(){onScroll();},false);
	}
	function onScroll() {
		for (var i = 0; i < inview.length; i++) {
			(function(i){
				if (inview[i].rendered == false) {
					var elmY = inview[i].elmY;
					var scrollY = scrolltop();
					if (elmY <= (scrollY + document.documentElement.clientHeight)) {
						(inview[i].action)();
						inview[i].rendered = true;
					}
				}
			})(i);
		}
	}
	//要素の位置を返す
	function offsettop(elm) {
		var offsettop = elm.offsetTop;
		if (elm.offsetParent) {
			while (elm = elm.offsetParent) {
				offsettop += elm.offsetTop;
			}
		}
		return offsettop;
	}
	//スクロール位置を返す
	function scrolltop() {
		if (document.body && document.body.scrollTop) {
			return document.body.scrollTop;
		}
		if (document.documentElement && document.documentElement.scrollTop) {
			return document.documentElement.scrollTop;
		}
		if (window.pageYOffset) {
			return window.pageYOffset;
		}
		return 0;
	}
})(window,document,inview);