diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/for-of/semantics-09.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/for-of/semantics-09.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,25 @@
+// The LHS of a for-of loop is not evaluated until after the .next() method returns.
+
+var s;
+function f() {
+    s += 'f';
+    return {};
+}
+
+// Test 1: .next() throws StopIteration right away. f is never called.
+s = '';
+for (f().x of [])
+    s += '.';
+assertEq(s, '');
+
+// Test 2: check proper interleaving of f calls, iterator.next() calls, and the loop body.
+function g() {
+    s += 'g';
+    yield 0;
+    s += 'g';
+    yield 1;
+    s += 'g';
+}
+for (f().x of g())
+    s += '.';
+assertEq(s, 'gf.gf.g');