1 files changed, 21 insertions, 0 deletions
diff --git a/js/src/tests/non262/Intl/unicode-bcp47-locale-ids-extlangs.js b/js/src/tests/non262/Intl/unicode-bcp47-locale-ids-extlangs.js
new file mode 100644
index 0000000000..7e9aae5519
--- /dev/null
+++ b/js/src/tests/non262/Intl/unicode-bcp47-locale-ids-extlangs.js
@@ -0,0 +1,21 @@
+// |reftest| skip-if(!this.hasOwnProperty("Intl"))
+
+// Unicode BCP 47 locale identifiers don't support extlang subtags.
+const invalid = [
+    // Two letter language code followed by extlang subtags.
+    "en-abc",
+    "en-abc-def",
+    "en-abc-def-ghi",
+
+    // Three letter language code followed by extlang subtags.
+    "und-abc",
+    "und-abc-def",
+    "und-abc-def-ghi",
+];
+
+for (let locale of invalid) {
+    assertThrowsInstanceOf(() => Intl.getCanonicalLocales(locale), RangeError);
+}
+
+if (typeof reportCompare === "function")
+    reportCompare(true, true);