Hide side bar when inactive, shows when mouse enters right screen. Reddit.

gistfile1.txt

var sideBarLength, rightSide, winLength, pointerX, sideShowing, transition;

winLength = window.innerWidth || window.innerLength;
sideBar = document.getElementsByClassName('side')[0];
rightSide = winLength - sideBar.clientWidth;
sideShowing = true;
transition = (function () {
    var vendors = ["Webkit", "Moz", "ms", "O"], result;
    for (var i = 0; i < vendors.length;) {
	if (vendors[i] + "Transition" in sideBar.style){
	    result = vendors[i] + "Transition";
	    return result;
	}
    }
    return "transition";
})();

sideBar.style[transition] = "width, 2s, ease-in-out";

window.onmousemove = function (event) {
    pointerX = event.clientX; 
    if (sideShowing && pointerX < rightSide) {
	window.setTimeout(function () {sideBar.style.width = "0px"}, 2000);
	sideShowing = false;
    } else {
	if (pointerX > rightSide + 200) {
	    sideBar.style.width = "300px";
	    sideShowing = true;
	}
    }
}