In computer programming, the async/await pattern is a syntactic feature of many programming languages that allows an asynchronous, non-blocking function to be structured in a way similar to an ordinary synchronous function. It is semantically related to the concept of a coroutine and is often implemented using similar techniques, and is primarily intended to provide opportunities for the program to execute other code while waiting for a long-running, asynchronous task to complete, usually represented by promises or similar data structures. The feature is found in C# 5.0, Python 3.5, Hack, Dart, Kotlin 1.1, Rust 1.39, Nim 0.9.4 and JavaScript ES2017, with some experimental work in extensions, beta versions, and particular implementations of Scala and C++.
