购物车没有tab时 不能结算

@@ -19,29 +19,31 @@ require('./good');
 
 lazyLoad($('img.lazy'));
 
-navHammer = new Hammer(document.getElementsByClassName('cart-nav')[0]);
-navHammer.on('tap', function(e) {
-    var $this = $(e.target).closest('li');
-
-    if ($this.hasClass('active')) {
-        return;
-    }
-
-    if (cartType === 'ordinary') {
-        cartType = 'advance';
-    } else {
-        cartType = 'ordinary';
-    }
-
-    $this.siblings('.active').removeClass('active');
-    $this.addClass('active');
-
-    //切换普通商品和预售商品购物车显示
-    $cartContent.toggleClass('hide');
-
-    //trigger lazyload
-    $(window).trigger('scroll');
-});
+if ($('.cart-nav').length > 0) {
+    navHammer = new Hammer(document.getElementsByClassName('cart-nav')[0]);
+    navHammer.on('tap', function(e) {
+        var $this = $(e.target).closest('li');
+
+        if ($this.hasClass('active')) {
+            return;
+        }
+
+        if (cartType === 'ordinary') {
+            cartType = 'advance';
+        } else {
+            cartType = 'ordinary';
+        }
+
+        $this.siblings('.active').removeClass('active');
+        $this.addClass('active');
+
+        //切换普通商品和预售商品购物车显示
+        $cartContent.toggleClass('hide');
+
+        //trigger lazyload
+        $(window).trigger('scroll');
+    });
+}
 
 $('.btn-balance').on('touchend', function() {
     window.location.href = '/cart/index/orderEnsure?cartType=' + cartType;