diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/arrow-functions/length.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/arrow-functions/length.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,11 @@
+// Arrow functions have a .length property like ordinary functions.
+
+assertEq((a => a).hasOwnProperty("length"), true);
+
+assertEq((a => a).length, 1);
+assertEq((() => 0).length, 0);
+assertEq(((a) => 0).length, 1);
+assertEq(((a, b) => 0).length, 2);
+
+assertEq(((...arr) => arr).length, 0);
+assertEq(((a=1, b=2) => 0).length, 0);