From 7e17c423d3828924634c824e3f3767d970bc3012 Mon Sep 17 00:00:00 2001
From: Cristian Necula <VirusZ@gmail.com>
Date: Tue, 22 Oct 2024 15:47:11 +0300
Subject: [PATCH] fix: infinite loop if effect schedules an update and then
 throws (#469)

Update lastValues before running the callback.

Fixes #468
---
 .changeset/witty-zoos-peel.md |  5 +++++
 src/create-effect.ts          |  6 ++++--
 test/use-effects.test.ts      | 21 +++++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/witty-zoos-peel.md

diff --git a/.changeset/witty-zoos-peel.md b/.changeset/witty-zoos-peel.md
new file mode 100644
index 0000000..341ff5c
--- /dev/null
+++ b/.changeset/witty-zoos-peel.md
@@ -0,0 +1,5 @@
+---
+"haunted": patch
+---
+
+Prevent infinite loops if effect schedules an update and then throws.
diff --git a/src/create-effect.ts b/src/create-effect.ts
index 20d99d9..b6a66f5 100644
--- a/src/create-effect.ts
+++ b/src/create-effect.ts
@@ -21,10 +21,12 @@ function createEffect(setEffects: (state: State, cb: Callable) => void) {
     }
 
     call(): void {
-      if(!this.values || this.hasChanged()) {
+      const hasChanged = !this.values || this.hasChanged();
+      this.lastValues = this.values;
+
+      if(hasChanged) {
         this.run();
       }
-      this.lastValues = this.values;
     }
 
     run(): void {
diff --git a/test/use-effects.test.ts b/test/use-effects.test.ts
index 8b93351..87195de 100644
--- a/test/use-effects.test.ts
+++ b/test/use-effects.test.ts
@@ -176,4 +176,25 @@ describe('useEffect', () => {
     expect(parentEffects).to.equal(2);
     expect(childEffects).to.equal(2);
   });
+
+  it("Avoids causing infinite loops when the callback schedules an update, but then throws an exception", async () => {
+    function App() {
+      const [state, setState] = useState(0);
+
+      useEffect(() => {
+        // an update is scheduled
+        setState((state) => state! + 1);
+        // an error is thrown
+        throw new Error("Unexpected error");
+      }, []);
+
+      return state;
+    }
+
+    customElements.define("infinite-loop-test", component(App));
+
+    const el = await fixture(html`<infinite-loop-test></infinite-loop-test>`);
+    expect(el).to.be.ok;
+    expect(el.shadowRoot!.textContent).to.equal("1");
+  });
 });