JS: prove that KT-8315 is no more reproducible

js/js.translator/testData/box/number/incDecOptimization.kt

@@ -0,0 +1,20 @@
+// EXPECTED_REACHABLE_NODES: 1029
+// CHECK_VARS_COUNT: function=test count=1
+
+class A {
+    var i = 23
+}
+
+fun test(a: A): String {
+    var x = ++a.i
+    if (x != 24) return "fail1: $x"
+
+    a.i++
+    if (a.i != 25) return "fail2: $a.i"
+
+    // a.i++, used as expression, requires temporary variable
+
+    return "OK"
+}
+
+fun box(): String = test(A())