uploadius_hover_zoom.user.js

// ==UserScript==
// @name        Uploadius Hover Zoom
// @namespace   uploadiushoverzoom
// @include     http://swololol.com/*
// @version     1
// @grant       none
// ==/UserScript==

window.onload = function() {
	var title = document.getElementsByTagName("h1");
	title[0].innerHTML = "<a style=\"text-decoration:none;color:#00f;\" href=\"http://swololol.com/ufi\">Uploadius (hoverzoom by @aearnus)</a>"
	var links = document.getElementsByTagName("a");
	var imageLinks = [];
	for(var i = 0; i < links.length; i++) {
		if(/\.(jpg|gif|png|jpeg)$/.test(links[i].href)) {
			imageLinks.push(links[i]);
		}
	}
	var documentHeight = Math.max(document.body.scrollHeight, document.body.offsetHeight, document.documentElement.clientHeight, document.documentElement.scrollHeight, document.documentElement.offsetHeight);
	//http://stackoverflow.com/questions/1145850/how-to-get-height-of-entire-document-with-javascript
	for(var i = 0; i < imageLinks.length; i++) {
		var currentLink = imageLinks[i];
		currentLink.onmouseenter = function(cursorEvent) {
			var x = cursorEvent.clientX;
			var y = cursorEvent.clientY;
			window.hoverImg = document.createElement("img");
			window.hoverImg.src = this.href;
			if(documentHeight - y < 300) {
				window.hoverImg.style = "position: absolute; top:" + (y+document.body.scrollTop-250) + "px; left:" + (x+document.body.scrollLeft+5) + "px; width: auto; max-height: 250px";
			} else {
				window.hoverImg.style = "position: absolute; top:" + (y+document.body.scrollTop) + "px; left:" + (x+document.body.scrollLeft+5) + "px; width: auto; max-height: 250px";
			}
			document.body.appendChild(window.hoverImg);
		}
		currentLink.onmouseleave = function() {
			document.body.removeChild(window.hoverImg);
			window.hoverImg = {};
		}
		currentLink.onmouseout = function() {
			document.body.removeChild(window.hoverImg);
			window.hoverImg = {};
		}
	}
}