docs: function start(options) {
  
          /**
           * 默认参数 {
           *     selector : <string> // 代理元素的选择器规则
           *     cacheMaxTime: <integer> //缓存存活时间，默认5min
           * }
           */
          var defaultOptions = {
              selector: "a,[data-href]",
              cacheMaxTime: 5 * 60 * 1000,
              pushState : true,
              layer : document.body
          };
  
          appOptions = merge(defaultOptions, options);
          cacheMaxTime = appOptions.cacheMaxTime;
          isPushState = appOptions.pushState;
          layer = getLayer(appOptions.layer);
  
          curPageUrl = getCurrentUrl();
  
          if(isPushState === true){
              // 绑定事件
              bindEvent();
          }
      }