function Page(obj) {
     this.obj = obj||{page:1,page_count: 0};
     this.z_page = 7;    // 一共顯示的頁(yè)碼數(shù)
     this.show_page = this.z_page-2; // 中間顯示多少個(gè)頁(yè)碼  必須是個(gè)基數(shù)好看
     this.fn = this.obj.block;
     this.init()
 }

Page.prototype.create = function () {
     // page:1 page_count 17
     // 保證被點(diǎn)擊的頁(yè)數(shù)在中間
     var ping = (this.show_page-1)/2; // 左右顯示的平均數(shù)  在中間
     var num = this.obj.page-ping; // 最小頁(yè)碼
     var endnum =  (this.obj.page+ping)>this.obj.page_count?this.obj.page_count:(this.obj.page+ping) // 最大頁(yè)碼
     console.log(endnum);
     var pageID = document.getElementById('pageID');
     var self= this;
     pageID.innerHTML = '';
     num = num<1?1:num;
     if (this.obj.page_count<= this.z_page) {
         alert('smallPage');
         this.smallPage()
     } else if( (this.obj.page+ping+1)>=this.obj.page_count) {// 還要加上最后一個(gè)   接近尾頁(yè)
         pageID.appendChild(this.nearBack())
         console.log('尾巴')

     } else if ((ping+2)>=(this.obj.page)) {  //3   接近首頁(yè)
         pageID.appendChild( this.nearHome())
         console.log('臨近首頁(yè)')
     }else {
         console.log(num,endnum);
         pageID.appendChild(this.centerPage(num,endnum));
     }
     document.onclick = function (event) {
         switch (event.target.className) {
             case 'previous':
                 self._previous();
                 break;
             case 'next':
                 self._next();
                 break;
             default:
                 self.clickLi(event.target);
         }
         self.fn(self.obj.page)
     }
 };

 Page.prototype.nearBack = function () {
     var oFragmeng = document.createDocumentFragment(); // 創(chuàng)建了一個(gè)文檔碎片
     var ul = document.createElement('ul')
     var Div = oFragmeng.appendChild(ul);
      Div.innerHTML = '<li>1</li><li>....</li>';
     for (var m=(this.obj.page_count- this.show_page);m<=this.obj.page_count;m++) {
         var li1 = document.createElement('li');
         li1.innerHTML = m;
         if (m===this.obj.page) {
             li1.className = 'active'
         }
         Div.appendChild(li1)
     }
    return oFragmeng.firstChild;
 };