refactor classes, add private, minor fixes

1-js/11-async/04-promise-error-handling/01-error-async/task.md

@@ -0,0 +1,11 @@
+# Error in setTimeout
+
+What do you think? Will the `.catch` trigger? Explain your answer.
+
+```js
+new Promise(function(resolve, reject) {
+  setTimeout(() => {
+    throw new Error("Whoops!");
+  }, 1000);
+}).catch(alert);
+```