diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/Array-of-length-setter.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/Array-of-length-setter.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,26 @@
+// Array.of calls a "length" setter if one is present.
+
+var hits = 0;
+var lastObj = null, lastVal = undefined;
+function setter(v) {
+    hits++;
+    lastObj = this;
+    lastVal = v;
+}
+
+// when the setter is on the new object
+function Pack() {
+    Object.defineProperty(this, "length", {set: setter});
+}
+Pack.of = Array.of;
+var pack = Pack.of("wolves", "cards", "cigarettes", "lies");
+assertEq(lastObj, pack);
+assertEq(lastVal, 4);
+
+// when the setter is on the new object's prototype
+function Bevy() {}
+Object.defineProperty(Bevy.prototype, "length", {set: setter});
+Bevy.of = Array.of;
+var bevy = Bevy.of("quail");
+assertEq(lastObj, bevy);
+assertEq(lastVal, 1);