Completed challenges from js-hard-parts course from frontendmasters

1. Callbacks and Higher-Order Functions contains set of completed tasks from http://csbin.io/callbacks
2. Closures, Scope, and ExecutionContext contains set of completed tasks from http://csbin.io/closures
3. Async contains set of completed tasks from http://csbin.io/async
4. OOP contains set of completed tasks from http://csbin.io/oop
5. Promises contains set of completed tasks from http://csbin.io/promises
6. Iterators contains set of completed tasks from http://csbin.io/iterators

Note: For practise first try to complete challenges, from the above links, by yourself, don't immediately look for solutions