Calling matchMedia during a MQL change event will not panic

1 files changed, 12 insertions, 6 deletions

diff --git a/components/script/dom/mediaquerylist.rs b/components/script/dom/mediaquerylist.rs
index c6e569b5e42..2545b911c7a 100644
--- a/components/script/dom/mediaquerylist.rs
+++ b/components/script/dom/mediaquerylist.rs
@@ -138,17 +138,23 @@ impl WeakMediaQueryListVec {
     /// Evaluate media query lists and report changes
     /// https://drafts.csswg.org/cssom-view/#evaluate-media-queries-and-report-changes
     pub fn evaluate_and_report_changes(&self) {
+        rooted_vec!(let mut mql_list);
         self.cell.borrow_mut().update(|mql| {
             let mql = mql.root().unwrap();
             if let MediaQueryListMatchState::Changed(_) = mql.evaluate_changes() {
-                let event = MediaQueryListEvent::new(&mql.global(),
-                                                     atom!("change"),
-                                                     false, false,
-                                                     mql.Media(),
-                                                     mql.Matches());
-                event.upcast::<Event>().fire(mql.upcast::<EventTarget>());
+                // Recording list of changed Media Queries
+                mql_list.push(JS::from_ref(&*mql));
             }
         });
+        // Sending change events for all changed Media Queries
+        for mql in mql_list.iter() {
+            let event = MediaQueryListEvent::new(&mql.global(),
+                                                 atom!("change"),
+                                                 false, false,
+                                                 mql.Media(),
+                                                 mql.Matches());
+            event.upcast::<Event>().fire(mql.upcast::<EventTarget>());
+        }
     }
 }