refactor classes, add private, minor fixes

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

@@ -0,0 +1,14 @@
+
+# Delay with a promise
+
+The built-in function `setTimeout` uses callbacks. Create a promise-based alternative.
+
+The function `delay(ms)` should return a promise. That promise should resolve after `ms` milliseconds, so that we can add `.then` to it, like this:
+
+```js
+function delay(ms) {
+  // your code
+}
+
+delay(3000).then(() => alert('runs after 3 seconds'));
+```