utils for transitioning between game and DOM elements

fade-in.js

function fadeIn(id,speed) {
	var element = document.getElementById(id);
    var op = 0.1;  // initial opacity
    element.style.visibility = 'visible';
	element.style.opacity = op;
    var timer = setInterval(function () {
        if (op >= 1){
            clearInterval(timer);
        }
        element.style.opacity = op;
        element.style.filter = 'alpha(opacity=' + op * 100 + ")";
        op = op * 1.5;
    }, speed);

}