Fade in and fade out javaScript functions

fade.js

//    fade.js
//    Fade in and fade out javaScript functions 
//
//    Copyright (C) 2016  Meena Erian
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU General Public License as published by
//    the Free Software Foundation, either version 3 of the License, or
//    (at your option) any later version.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU General Public License for more details.
//
//   You should have received a copy of the GNU General Public License
//   along with this program.  If not, see <http://www.gnu.org/licenses/>.

function fadeIn(elem) {
 	elem.style.opacity = 0;
	var lid = setInterval(nextFadeIn,50, elem);
	function nextFadeIn(elem) {
		if(elem.style.opacity>=1) {
			elem.style.opacity = 1;
			clearInterval(lid);
		}
		else elem.style.opacity = parseFloat(elem.style.opacity) + 0.1;
	}
}

function fadeOut(elem) {
 	elem.style.opacity = 1;
	var lid = setInterval(nextFadeOut,50, elem);
	function nextFadeOut(elem) {
		if(elem.style.opacity<=0) {
			elem.style.opacity = 0;
			clearInterval(lid);
		}
		else elem.style.opacity = parseFloat(elem.style.opacity) - 0.1;
	}
}