TypeScript

TypeScript's type system is very powerful—it can represent a lot of JavaScript constructs as a result. Here's how to type a function with an extra property.

Using mapped types, making factories for test data is a cinch. And I can use mapped types to provide guarantees you simply can't get in a dynamic language.

Use these key steps to create strongly typed immutable records in TypeScript with Immutable.js.

The new TypeScript version, 2.0, has some new additions that are great for Redux development in React: type narrowing for tagged unions.