fix(fast-element): do not notify splices for changes pre-subscription…

… (v2) (#6006) * fix(fast-element): do not notify splices for changes pre-subscription * Change files Co-authored-by: EisenbergEffect <[email protected]>
microsoft · May 31, 2022 · bbbafc2 · bbbafc2
1 parent a5db4c3
commit bbbafc2
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Showing 4 changed files with 34 additions and 4 deletions.
diff --git a/change/@microsoft-fast-element-65662448-c859-4bfd-b06d-a52379348361.json b/change/@microsoft-fast-element-65662448-c859-4bfd-b06d-a52379348361.json
@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "fix(fast-element): do not notify splices for changes pre-subscription",
+  "packageName": "@microsoft/fast-element",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}
diff --git a/packages/web-components/fast-element/src/observation/arrays.spec.ts b/packages/web-components/fast-element/src/observation/arrays.spec.ts
@@ -336,6 +336,24 @@ describe("The ArrayObserver", () => {
         expect(changeArgs![0].removed).members([]);
         expect(changeArgs![0].index).equal(0);
     });
+
+    it("should not deliver splices for changes prior to subscription", async () => {
+        ArrayObserver.enable();
+        const array = [1,2,3,4,5];
+        const observer = Observable.getNotifier(array);
+        let wasCalled = false;
+
+        array.push(6);
+        observer.subscribe({
+            handleChange() {
+                wasCalled = true;
+            }
+        });
+
+        await Updates.next();
+
+        expect(wasCalled).to.be.false;
+    })
 });
 
 describe("The array length observer", () => {

diff --git a/packages/web-components/fast-element/src/observation/arrays.ts b/packages/web-components/fast-element/src/observation/arrays.ts
@@ -423,6 +423,11 @@ class DefaultArrayObserver extends SubscriberSet implements ArrayObserver {
         setNonEnumerable(subject, "$fastController", this);
     }
 
+    public subscribe(subscriber: Subscriber): void {
+        this.flush();
+        super.subscribe(subscriber);
+    }
+
     public addSplice(splice: Splice) {
         if (this.splices === void 0) {
             this.splices = [splice];

diff --git a/packages/web-components/fast-element/src/observation/notifier.ts b/packages/web-components/fast-element/src/observation/notifier.ts
@@ -150,22 +150,22 @@ export class SubscriberSet implements Notifier {
      */
     public notify(args: any): void {
         const spillover = this.spillover;
-        const source = this.source;
+        const subject = this.subject;
 
         if (spillover === void 0) {
             const sub1 = this.sub1;
             const sub2 = this.sub2;
 
             if (sub1 !== void 0) {
-                sub1.handleChange(source, args);
+                sub1.handleChange(subject, args);
             }
 
             if (sub2 !== void 0) {
-                sub2.handleChange(source, args);
+                sub2.handleChange(subject, args);
             }
         } else {
             for (let i = 0, ii = spillover.length; i < ii; ++i) {
-                spillover[i].handleChange(source, args);
+                spillover[i].handleChange(subject, args);
             }
         }
     }