Merge pull request #2103 from immutable-js/merge-empty-record

jdeniau · web-flow · commit ec2ba80fe791 · 2025-05-06T00:22:21.000+02:00
diff --git a/__tests__/merge.ts b/__tests__/merge.ts
@@ -329,4 +329,21 @@ describe('merge', () => {
     const b = Map({ a: Map([[0, Map({ y: 2 })]]) });
     expect(mergeDeep(a, b)).toEqual({ a: Map([[0, Map({ y: 2 })]]) });
   });
+
+  it('works with an empty Record', () => {
+    class MyRecord extends Record({ a: 1 }) {}
+
+    const myRecord = new MyRecord();
+    expect(merge(myRecord, { a: 4 })).toEqual(
+      new MyRecord({
+        a: 4,
+      })
+    );
+
+    class MyEmptyRecord extends Record({}) {}
+
+    const myEmptyRecord = new MyEmptyRecord();
+    // merging with an empty record should return the same empty record instance
+    expect(merge(myEmptyRecord, { a: 4 })).toBe(myEmptyRecord);
+  });
 });
diff --git a/src/methods/merge.js b/src/methods/merge.js
@@ -1,6 +1,7 @@
 import { KeyedCollection } from '../Collection';
 import { NOT_SET } from '../TrieUtils';
 import { update } from '../functional/update';
+import { isRecord } from '../predicates/isRecord';
 
 export function merge(...iters) {
   return mergeIntoKeyedWith(this, iters);
@@ -29,7 +30,9 @@ function mergeIntoKeyedWith(collection, collections, merger) {
     !collection.__ownerID &&
     iters.length === 1
   ) {
-    return collection.constructor(iters[0]);
+    return isRecord(collection)
+      ? collection // Record is empty and will not be updated: return the same instance
+      : collection.constructor(iters[0]);
   }
   return collection.withMutations((collection) => {
     const mergeIntoCollection = merger
