无聊写了一个JS下拉加载插件，有需要的可以下载。

// 使用

// new ManDownLoad("#ul","json/load.json",function(data,obj){

//   var str = "";

//   data.data.forEach(function(item,index){

//      str += "<li>" + item.title + "</li>";

//   });

//   return str;

// },{

//  type:"POST",

//  data:{

//    "hello":"world",

//    "fa":"bbb"

//  }

// });

;function ManDownLoad(element,url,callback,obj){

  this.element = element;

  if((typeof element)==="string"){

    this.element = document.querySelector(element);

  }

  this.url = url;

  this.callback = callback;

  var options = {

    type:"GET",

    distance:0,

    dataType:"json",

    data:{}

  };

  this.config = this.extend(options,obj);

  this.init();

};

ManDownLoad.prototype = {

  init:function(){

    var _this = this;

    this.isBottom();

    window.addEventListener("scroll",this.isBottom);

  },

  // 判断是否到达底部

  isBottom:function(){

    var _this = this;

    var scrollH = null,

        clientHeight = null,

        scrollTop = null,

        h = 0;

    scrollH = document.body.scrollHeight||document.documentElement.scrollHeight;

    clientHeight = window.innerHeight;

    scrollTop = document.body.scrollTop||document.documentElement.scrollTop;

    h = clientHeight + scrollTop;

    if(h>=scrollH-_this.config.distance){

      _this.ajax();

    }

  },

  // 发送AJAX请求

  ajax:function(){

    var _this = this;

    var xhr = new XMLHttpRequest();

    var data = null;

    xhr.open(this.config.type,this.url,true);

    xhr.onreadystatechange = function(){

      if(xhr.readyState==4&&xhr.status==200){

        if(_this.config.dataType==="json"){

          data = _this.callback(JSON.parse(xhr.responseText),_this);

        }else{

          data = _this.callback(xhr.responseText,_this);

        }

        if(data===false){

        	window.removeEventListener("scroll",_this.isBottom);

        }

        _this.addHTML(data,function(){

          _this.isBottom();

        });

      }

    }

    xhr.send(_this.toFormStr(_this.config.data));

  },

  addHTML:function(data,callback){

  	if(!data)return;

    if((typeof data)==="string"){

        this.element.innerHTML += data;

    }else{

        this.element.appendChild(data);

    }

    callback&&callback();

  },

  toFormStr:function(obj){

  	var str = "";

	for(var k in obj){

		str += k + "=" + obj[k] + "&";

	}

	return str.slice(0,-1);

  },

  extend:function(obj,obj2){

  	if(!obj)return obj2;

  	for(var k in obj2){

		obj[k] = obj2[k];

	}

	return obj;

  }

};