;(function(){
	function mobileMedia(options){
        this.options = options;
        if(typeof this.meta!='function'){ //不判断则实例一次初始化一次
            mobileMedia.prototype.meta=function(){
                return 'aaa';
            }
        }
	}
	var mobile=new mobileMedia({
		rootSize:20
	})
	 document.write(mobile.meta());
}(window,document));