//用于匹配类名存在与否
function reg(name){
    return new RegExp(‘(^|\\s)‘+name+‘(\\s+|$)‘);
}

//hasClass addClass removeClass toogleClass
var hasClass,addClass,removeClass;
if(‘classList‘ in document.documentElement){
    hasClass=function(obj,cname){
        return obj.classList.contains(cname);
    };
    addClass=function(obj,cname){
        obj.classList.add(cname);
    };
    removeClass=function(obj,cname){
        obj.classList.remove(cname);
    };
    toggleClass=function(obj,cname){
        obj.classList.toggle(cname);
    };
}else{
    hasClass=function(obj,cname){
        return reg(cname).test(obj.className);
    };
    addClass=function(obj,cname){
        if(!hasClass(obj,cname)){
            obj.className=obj.className+‘ ‘+cname;    
        }
    };
    removeClass=function(obj,cname){
        obj.className=obj.className.replace(reg(cname),‘ ‘);
    };
    toggleClass=function(obj,cname){
        var toggle=hasClass(obj,cname)?removeClass:addClass;
        toggle(obj,cname);
    };
}

//true
document.body.classList.toString() === document.body.className;

//addClass
DOMTokenList.prototype.addClass=function(str){
  tts.split(‘ ‘).forEach(function(c){
    this.add(c);
  }.bind(this));
  return this;
}

//removeClass
DOMTokenList.prototype.removeClass=function(str){
  tts.split(‘ ‘).forEach(function(t){
    this.remove(t);
  }.bind(this));
  return this;
}

//removeClass
DOMTokenList.prototype.toggleClass=function(str){
  tts.split(‘ ‘).forEach(function(t){
    this.toggle(t);
  }.bind(this));
  return this;
}