refactor classes, add private, minor fixes

1-js/11-async/02-promise-basics/02-delay-promise/solution.md

@@ -0,0 +1,9 @@
+```js run
+function delay(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+delay(3000).then(() => alert('runs after 3 seconds'));
+```
+
+Please note that in this task `resolve` is called without arguments. We don't return any value from `delay`, just ensure the delay.