diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testArrayConcat.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testArrayConcat.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+
+var x = Array(4);
+x[0] = 1;
+x[1] = 2;
+x[2] = 3;
+var y = x.concat();
+assertEq(y[3], undefined);
+
+var z = x.concat(/abc/).pop();
+assertEq(z.source, "abc");