TypeScript is an open source programming language written on top of JavaScript to support types. TypeScript is not a completely new language and is not intended to replace JavaScript in anyway. It adheres to all principles of JavaScript and just adds types on top of it. If you are already good at JavaScript, it won’t take you much time to learn TypeScript.
The TypeScript team is working very hard to keep the language updated with the latest specifications of JavaScript. Most of the proposed features of ES6 and ES7 are implemented by TypeScript. They get converted into their ES5 equivalent when the TypeScript files are transpiled. This makes it possible to use the latest features of JavaScript even when the browsers have not implemented them natively.