1、hasClass
function hasClass(elem, cls){
cls = cls || ‘‘;
if(cls.replace(/\s/g, ‘‘).length == 0) return false;
return new RegExp(‘ ‘ + cls + ‘ ‘).test(‘ ‘ + elem.className + ‘ ‘);
}2、addClass
function addClass(elem, cls){
if(!hasClass(elem, cls)){
elem.className += ‘ ‘ + cls;
}
}3、removeClass
function removeClass(elem, cls){
if(hasClass(elem, cls)){
var newClass = ‘ ‘ + elem.className.replace(/[\t\r\n]/g, ‘‘) + ‘ ‘;
while(newClass.indexOf(‘ ‘ + cls + ‘ ‘) >= 0){
newClass = newClass.replace(‘ ‘ + cls + ‘ ‘, ‘ ‘);
}
elem.className = newClass.replace(/^\s+|\s+$/g, ‘‘);
}
}原生JS实现hasClass,addClass,removeClass
原文：http://qings.blog.51cto.com/4857138/1562222