check if element is in viewport

inViewport.js

var docElem = window.document.documentElement;
	function getViewportH() {
		var client = docElem['clientHeight'],
			inner = window['innerHeight'];
		 
		if( client < inner )
			return inner;
		else
			return client;
	}
 
	function scrollY() {
		return window.pageYOffset || docElem.scrollTop;
	}
 
	// http://stackoverflow.com/a/5598797/989439
	function getOffset( el ) {
		var offsetTop = 0, offsetLeft = 0;
		do {
			if ( !isNaN( el.offsetTop ) ) {
				offsetTop += el.offsetTop;
			}
			if ( !isNaN( el.offsetLeft ) ) {
				offsetLeft += el.offsetLeft;
			}
		} while( el = el.offsetParent );
 
		return {
			top : offsetTop,
			left : offsetLeft
		};
	}
 
	function inViewport( el, h ) {
		var elH = el.offsetHeight,
			scrolled = scrollY(),
			viewed = scrolled + getViewportH(),
			elTop = getOffset(el).top,
			elBottom = elTop + elH,
			// if 0, the element is considered in the viewport as soon as it enters.
			// if 1, the element is considered in the viewport only when it's fully inside
			// value in percentage (1 >= h >= 0)
			h = h || 0;
 
		return (elTop + elH * h) <= viewed && (elBottom) >= scrolled;
	}