show footer when document ready and fix bug when it can not find goodsDiscount. code review by XWG

@@ -12,13 +12,17 @@ var goodsSwiper,
     $discountFolder = $('.goodsDiscount .discount-folder'),
     $discountArrow = $('.goodsDiscount .first-item span');
 
-var goodsDiscountHammer = new Hammer(document.getElementById('goodsDiscount'));
+var goodsDiscountEl = document.getElementById('goodsDiscount'),
+    goodsDiscountHammer = goodsDiscountEl && new Hammer(goodsDiscountEl);
 
 require('./desc');
 require('./comments-consults');
 
 //add extra marign-bottom for footer to show the yoho copyright
-window.reMarginFooter('.cart-bar');
+
+function showFooter() {
+    window.reMarginFooter('.cart-bar');
+}
 
 lazyLoad($('img.lazy'));
 
@@ -40,15 +44,19 @@ if (0 === $('.goodsDiscount .discount-folder').children().length) {
 }
 
 //goods-discount下拉按钮点击事件
-goodsDiscountHammer.on('tap', function(e) {
-    if ($discountFolder.is(':hidden')) {
-        $discountArrow.removeClass('icon-down').addClass('icon-up').html('');
-        $discountFolder.slideDown();
-    } else {
-        $discountArrow.removeClass('icon-up').addClass('icon-down').html('');
-        $discountFolder.slideUp();
-    }
-    return false;
-});
+if (goodsDiscountHammer) {
+    goodsDiscountHammer.on('tap', function(e) {
+        if ($discountFolder.is(':hidden')) {
+            $discountArrow.removeClass('icon-down').addClass('icon-up').html('');
+            $discountFolder.slideDown();
+        } else {
+            $discountArrow.removeClass('icon-up').addClass('icon-down').html('');
+            $discountFolder.slideUp();
+        }
+        return false;
+    });
+}
 
 require('./like');
+
+$(document).ready(showFooter);