[JavaScript] Change callback function to async/await

This video shows you how to replace callback function with async/await.

The example program used in this video gets the weather data from public API.
The callback function that is called after getting the weather data is replaced with the function called with "await" in this video.

You would be able to understand following things through this video.
- What is the callback function?
- How to replace it with async/await approach
- What is the promise?
- Behavior of each approach (callback and async/await)