From 749d1fc9422d7e35276da3097480707c59263e72 Mon Sep 17 00:00:00 2001
From: Jukka Kurkela <jukka.kurkela@gmail.com>
Date: Wed, 19 May 2021 02:24:35 +0300
Subject: [PATCH] Fix animations when data is replaced (#9120)

---
 src/core/core.datasetController.js         | 8 ++++----
 test/specs/core.datasetController.tests.js | 2 ++
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/core/core.datasetController.js b/src/core/core.datasetController.js
index 6f1dc0efa..dbf08e77f 100644
--- a/src/core/core.datasetController.js
+++ b/src/core/core.datasetController.js
@@ -332,16 +332,15 @@ export default class DatasetController {
       if (_data) {
         // This case happens when the user replaced the data array instance.
         unlistenArrayEvents(_data, me);
-        // Discard old elements, parsed data and stacks
+        // Discard old parsed data and stacks
         const meta = me._cachedMeta;
         clearStacks(meta);
         meta._parsed = [];
-        meta.data = [];
       }
       if (data && Object.isExtensible(data)) {
         listenArrayEvents(data, me);
-        me._syncList = [];
       }
+      me._syncList = [];
       me._data = data;
     }
   }
@@ -933,7 +932,8 @@ export default class DatasetController {
       me._insertElements(numMeta, numData - numMeta, resetNewElements);
     } else if (numData < numMeta) {
       me._removeElements(numData, numMeta - numData);
-    } else if (count) {
+    }
+    if (count) {
       // TODO: It is not optimal to always parse the old data
       // This is done because we are not detecting direct assignments:
       // chart.data.datasets[0].data[5] = 10;
diff --git a/test/specs/core.datasetController.tests.js b/test/specs/core.datasetController.tests.js
index 773bbf54e..dfc2dd8d5 100644
--- a/test/specs/core.datasetController.tests.js
+++ b/test/specs/core.datasetController.tests.js
@@ -392,12 +392,14 @@ describe('Chart.DatasetController', function() {
 
     expect(meta.data.length).toBe(6);
     expect(meta._parsed.map(p => p.y)).toEqual(data0);
+    const point0 = meta.data[0];
 
     chart.data.datasets[0].data = data1;
     chart.update();
 
     expect(meta.data.length).toBe(3);
     expect(meta._parsed.map(p => p.y)).toEqual(data1);
+    expect(meta.data[0]).toEqual(point0);
 
     data1.push(9);
     chart.update();
-- 
2.47.3