1 files changed, 15 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/collections/Map-set-undefined.js b/js/src/jit-test/tests/collections/Map-set-undefined.js
new file mode 100644
index 0000000000..44ad134a99
--- /dev/null
+++ b/js/src/jit-test/tests/collections/Map-set-undefined.js
@@ -0,0 +1,15 @@
+// Setting a Map key to undefined, or a missing argument, isn't the same as deleting it.
+
+var m = new Map;
+m.set(42, undefined);
+assertEq(m.has(42), true);
+assertEq(m.get(42), undefined);
+
+m.set(42, "wrong");
+m.set(42);
+assertEq(m.has(42), true);
+assertEq(m.get(42), undefined);
+
+m.set();
+assertEq(m.has(undefined), true);
+assertEq(m.get(undefined), undefined);