[JS IR] Support per-file mode and ES modules

js/js.translator/testData/box/native/eval.kt

@@ -1,6 +1,5 @@
 // SKIP_MINIFICATION
 
-@JsExport
 val top = "TOP LEVEL"
 
 fun box(): String {
@@ -10,8 +9,10 @@ fun box(): String {
 
     assertEquals(5, eval("3 + 2"))
 
-    val PACKAGE = "JS_TESTS"
-    assertEquals(top, eval("$PACKAGE.top"))
+    if (testUtils.isLegacyBackend()) {
+        val PACKAGE = "JS_TESTS"
+        assertEquals(top, eval("$PACKAGE.top"))
+    }
 
     return "OK"
 }