diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/arguments/defaults-basic.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/arguments/defaults-basic.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,35 @@
+function f1(a, bIs, b=3) {
+    assertEq(a, 1);
+    assertEq(b, bIs);
+}
+assertEq(f1.length, 2);
+f1(1, 3);
+f1(1, 42, 42);
+f1(1, 3, undefined);
+function f2(a, bIs, cIs, b=3, c=4) {
+    assertEq(a, 1);
+    assertEq(b, bIs);
+    assertEq(c, cIs);
+}
+assertEq(f2.length, 3);
+f2(1, 3, 4);
+f2(1, 42, 4, 42);
+f2(1, 42, 43, 42, 43);
+f2(1, 3, 4, undefined);
+f2(1, 42, 4, 42, undefined);
+f2(1, 3, 42, undefined, 42);
+function f3(a, b, c=4) {
+    assertEq(a, 1);
+    assertEq(b, undefined);
+    assertEq(c, 4);
+}
+f3(1);
+function f4(a, bIs, cIs, b=3, c) {
+    assertEq(a, 1);
+    assertEq(b, bIs);
+    assertEq(c, cIs);
+}
+assertEq(f4.length, 3);
+f4(1, 3, undefined);
+f4(1, 4, undefined, 4);
+f4(1, 4, 5, 4, 5);