Master modern asynchronous programming in javascript. Learn the basics of async functions and Promises, then the common patterns that emerge when using asyncawait. Know how to write code that handles edge cases and concurrency right. Asynchronous programming is everywhere in javascript. This is the result of the fundamental choices that define how it works. In other languages, you can use multiple threads and that allows synchronous waiting, a crucial feature missing from javascript. It is by design single-threaded and a wait operation stops everything, just think of the case where a long calculation freezes the UI.