Fix MutationObserver infinite loop bugs (#3173)

The code was misindented relative to the spec. Fixes #3096. Fixes #3172.
jsdom · Apr 9, 2021 · 2f41466 · 2f41466
1 parent b232f2a
commit 2f41466
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Showing 2 changed files with 57 additions and 14 deletions.
diff --git a/lib/jsdom/living/helpers/mutation-observers.js b/lib/jsdom/living/helpers/mutation-observers.js
@@ -152,21 +152,21 @@ function notifyMutationObservers() {
       node._registeredObserverList = node._registeredObserverList.filter(registeredObserver => {
         return registeredObserver.source !== mo;
       });
+    }
 
-      if (records.length) {
-        try {
-          const moWrapper = idlUtils.wrapperForImpl(mo);
-          mo._callback.call(
-            moWrapper,
-            records.map(idlUtils.wrapperForImpl),
-            moWrapper
-          );
-        } catch (e) {
-          const { target } = records[0];
-          const window = target._ownerDocument._defaultView;
-
-          reportException(window, e);
-        }
+    if (records.length > 0) {
+      try {
+        const moWrapper = idlUtils.wrapperForImpl(mo);
+        mo._callback.call(
+          moWrapper,
+          records.map(idlUtils.wrapperForImpl),
+          moWrapper
+        );
+      } catch (e) {
+        const { target } = records[0];
+        const window = target._ownerDocument._defaultView;
+
+        reportException(window, e);
       }
     }
   }

diff --git a/test/web-platform-tests/to-upstream/dom/nodes/MutationObserver-callback-tricky.html b/test/web-platform-tests/to-upstream/dom/nodes/MutationObserver-callback-tricky.html
@@ -0,0 +1,43 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Certain actions within the callback does not lead to infinite loop</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<body>
+<script>
+  "use strict";
+
+  promise_test(() => {
+    let called = 0;
+    const div1 = document.createElement("div");
+    document.body.appendChild(div1);
+    const m = new MutationObserver(() => {
+      called++;
+      const div2 = document.createElement("div");
+      document.body.appendChild(div2);
+      m.observe(div2, { attributes: true });
+    });
+    m.observe(div1, { attributes: true });
+    div1.setAttribute("data-test", "test");
+    return Promise.resolve().then(() => {
+      assert_equals(called, 1, "times callback called");
+    });
+  }, "Calling observe in callback should not lead to more calls");
+
+  promise_test(() => {
+    let called = 0;
+    const div1 = document.createElement("div");
+    document.body.appendChild(div1);
+    const m = new MutationObserver(() => {
+      called++;
+      m.disconnect();
+      m.observe(div1, { attributes: true });
+    });
+    m.observe(div1, { attributes: true });
+    div1.setAttribute("data-test", "test");
+    return Promise.resolve().then(() => {
+      assert_equals(called, 1, "times callback called");
+    });
+  }, "Disconnect and re-observe in callback should not lead to more calls");
+</script>
+