diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testBug586866.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testBug586866.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,16 @@
+var magic = 8;
+
+var obj = {};
+for (var i = 1; i <= magic; ++i)
+    obj[i] = "a";
+
+function func() {
+    var i = 1;
+    while (i in obj) {
+        ++i;
+    }
+    return i - 1;
+}
+assertEq(func(), magic);
+assertEq(func(), magic);
+assertEq(func(), magic);