TypeScript
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript.
Site: http://www.typescriptlang.org
Books
Deep Dive in TypeScript
The definitive guide to TypeScript. Dive into all the details that a JavaScript developer needs to know to be a great TypeScript developer.
Typescript Succinctly
Jump into Microsoft's open-source superset of JavaScript with TypeScript Succinctly.