DatePicker: fix toDate, fixed #2538

packages/date-picker/src/util/index.js

@@ -13,7 +13,7 @@ export const equalDate = function(dateA, dateB) {
 };
 
 export const toDate = function(date) {
-  return isDate(date) ? date : null;
+  return isDate(date) ? new Date(date) : null;
 };
 
 export const isDate = function(date) {