Detects if an element is in the viewport and then displays it

inView.js

/*
	requires : 
	    underscore js
	    event subscriber
*/

inView = function (element) {

	var self = this,
		type,
		overflow = 0,

		initialise = function() {

			type = element.getAttribute('data-view-type');

			SD.scroll.addSubscriber('scroll', _.throttle(function() {
				var h = element.offsetHeight,
					x = elementInViewport(element,h);
					isInview(element,x);
			}, 25));

			var h = element.offsetHeight,
				x = elementInViewport(element,h);
					isInview(element,x);
		},

		isInview = function(el,visible){

			if( type == 'is-in-view') {

				if(visible){
					el.style.visibility = '';
				} else {
					el.style.visibility = 'hidden';
				}

			} 

		},

		elementInViewport = function(el,h) {

		var rect = el.getBoundingClientRect(),
			view = false,

			topInViewport =   rect.top - window.innerHeight;
			bottomInViewport = window.innerHeight - rect.bottom;


			if(topInViewport < overflow ) {
				view = true;
			}

			if( bottomInViewport > (window.innerHeight +overflow)){
				view = false;
			}

			return view;

		};

	if(element) {
		initialise();
	}


	return this;
};