It is better to learn the latest version of TypeScript.
View What's new
in order of release of new versions.
If you plan to develop with Angular.
TypeScript relevant. He recently started his mastering and use delivers greater UDOVOLSTVIE in the development rather than pure JS, which is disgusting. The output is still the same JS (it compiles tsc), but thanks to strong typing eliminates a large number of errors at the coding stage (which will not compile when Mesopotamia types (except any)).