merge code

@@ -10,8 +10,6 @@ var $footer = $('#yoho-footer'),
     $yohoPage = $('.yoho-page'),
     $header = $('.yoho-header');
 
-var backToTopHammer;
-
 function cookie(name) {
     var cookies = document.cookie,
         cookieVal,
@@ -132,8 +130,9 @@ function reMarginFooter(fixedElement) {
 (function() {
     var $op = $footer.children('.op-row');
 
-    var user = getUser(),
-        goTopHammer;
+    var user = getUser();
+
+    var backToTopHammer;
 
     rePosFooter(); //计算底部位置
 
@@ -154,17 +153,12 @@ function reMarginFooter(fixedElement) {
             '<a href="http://m.yohobuy.com/passport/signout/index?token=' + user[3] + '">退出</a>'
         );
     }
-    goTopHammer = new Hammer($op.find('.back-to-top')[0]);
-    goTopHammer.on('tap', function(e) {
-        $(window).scrollTop(0);
-        e.srcEvent.preventDefault();
-        return false;
-    });
 
     if ($op.find('.back-to-top').length > 0) {
-        backToTopHammer = new Hammer(document.getElementsByClassName('back-to-top')[0]);
+        backToTopHammer = new Hammer($op.find('.back-to-top')[0]);
         backToTopHammer.on('tap', function(e) {
             $(window).scrollTop(0);
+            e.srcEvent.preventDefault();
             return false;
         });
     }