From 6b607f37cf60b5121278885d04abaad3683019f6 Mon Sep 17 00:00:00 2001
From: Endi Modric <endi.modric@outlook.com>
Date: Fri, 8 Feb 2019 00:48:32 +0100
Subject: [PATCH] [DatePicker] fix onChange on month change after initial day
 selection (#3343)

* fix onChange doesn't fire on month change after initial day selection
Fixes #3340

* change !== to != operator

* add test onChange fired when month is changed for uncontrolled datepicker
---
 packages/datetime/src/datePicker.tsx       |  2 +-
 packages/datetime/test/datePickerTests.tsx | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/packages/datetime/src/datePicker.tsx b/packages/datetime/src/datePicker.tsx
index f08b0fc8d7..a5cdd9650c 100644
--- a/packages/datetime/src/datePicker.tsx
+++ b/packages/datetime/src/datePicker.tsx
@@ -246,7 +246,7 @@ export class DatePicker extends AbstractPureComponent<IDatePickerProps, IDatePic
                 selectedDay: day.getDate(),
             });
         }
-        if (this.state.value == null || this.state.value.getMonth() !== day.getMonth()) {
+        if (this.state.value != null && this.state.value.getMonth() !== day.getMonth()) {
             this.ignoreNextMonthChange = true;
         }
 
diff --git a/packages/datetime/test/datePickerTests.tsx b/packages/datetime/test/datePickerTests.tsx
index 6005c3d99e..dc9b712658 100644
--- a/packages/datetime/test/datePickerTests.tsx
+++ b/packages/datetime/test/datePickerTests.tsx
@@ -413,6 +413,16 @@ describe("<DatePicker>", () => {
             assert.isTrue(onChange.calledOnce);
         });
 
+        it("onChange fired when month is changed", () => {
+            const onChange = sinon.spy();
+            const { getDay, clickNextMonth } = wrap(<DatePicker onChange={onChange} />);
+            assert.isTrue(onChange.notCalled);
+            getDay().simulate("click");
+            assert.isTrue(onChange.calledOnce, "expected onChange called");
+            clickNextMonth();
+            assert.isTrue(onChange.calledTwice, "expected onChange called again");
+        });
+
         it("selected day updates are automatic", () => {
             const { assertSelectedDays, getDay } = wrap(<DatePicker />);
             assertSelectedDays();