自己遇到业务的时候可以自己封装一个插件！

//==1.前面加入分号，用（）包裹
;(function($, window, document, undefined){

    //==2 pluginName
    var pluginName = "navScrollSpy";
    //==3 defaults options
    var defaults = {
        navContainer: '#nav',  //外部容器
        navItems: 'a'     //元素
    };
    //==4.定义私有对象
    function navScrollSpy(element, options){
        this.element = element;             //获得id=#nav
        this.$ele = $(element);             //获得$("#nav")
        this.$win = $(window);              //获取window
      //==5.拓展对象
        this.options = $.extend({}, defaults, options);   //得到参数值

        this._defaults = defaults;
        this._name = pluginName;

        this.boxs = {};    //定义一个对象用来存放box的top值
        this.init();
    };
  //==5.为原型添加方法
    navScrollSpy.prototype = {
        init: function(){
            //得到a元素
            this.$a = this.$ele.find(this.options.navItems);
            //得到内容区Box的top值
            this.getBoxTop();

            //点击切换导航按钮样式,更改上下文this
            this.$a.on("click", $.proxy(this.clickSwitch,this));

            //滚动切换导航按钮
            this.$win.on("scroll",$.proxy(this.scrolling,this));

            //当页面重置时会发生问题？
            return this;
        },

        //导航固定
        fixNav: function(){
            var st = $(window).scrollTop();
            var $nav = $(this.options.navContainer)
            var fixValue = this.options.oldTop;
            if(st >= fixValue){
                $nav.css({
                    "position":"fixed",
                    "top" : this.options.newTop+"px"
                });
            }else{
                $nav.css({
                    "position":"absolute",
                    "top" : fixValue+"px"
                });
            }
        }
    };
    //==6.拓展方法
    $.fn.navScrollSpy = function(options){
        return this.each(function(){
            if(!$.data(this, "plugin_"+pluginName)){
                $.data(this, "plugin_"+pluginName,new navScrollSpy(this, options));
            }
        });
    };
})(jQuery, window, document);