Also, TypeScript 2.1 builds on TypeScript 2.0's use of control flow analysis to track types through a program. There will be deeper examination of the type of any variable that could be destined for a better type. With the improvement, types will be inferred based on whatever is assigned afterward.
Async/await, or downlevel async functions, is featured in the release candidate. It "allows users to write code around promises without needing to use callbacks," Rosenwasser said. "Async functions can be written in a style that looks synchronous, but acts asynchronously, using the await keyword." This capability was supported prior to version 2.1, but only when targeting ES2015. "TypeScript 2.1 brings the capability to ES3 and ES5 runtimes, meaning you'll be free to take advantage of it no matter what environment you're using," said Rosenwasser.