[Fix] stringify: when arrayFormat is comma, respect serializeDate

Fixes #364.

Author: ljharb

lib/stringify.js

@@ -75,7 +75,12 @@ var stringify = function stringify(
     } else if (obj instanceof Date) {
         obj = serializeDate(obj);
     } else if (generateArrayPrefix === 'comma' && isArray(obj)) {
-        obj = obj.join(',');
+        obj = utils.maybeMap(obj, function (value) {
+            if (value instanceof Date) {
+                return serializeDate(value);
+            }
+            return value;
+        }).join(',');
     }
 
     if (obj === null) {

test/stringify.js

@@ -595,6 +595,18 @@ test('stringify()', function (t) {
             'custom serializeDate function called'
         );
 
+        st.equal(
+            qs.stringify(
+                { a: [date] },
+                {
+                    serializeDate: function (d) { return d.getTime(); },
+                    arrayFormat: 'comma'
+                }
+            ),
+            'a=' + date.getTime(),
+            'works with arrayFormat comma'
+        );
+
         st.end();
     });