Typescript presentation from the Belgian Visual Studio User Group.

1. TypeScript = JavaScript (almost)
done right
Maurice de Beijer

2. Who am I
 Maurice de Beijer
 The Problem Solver
 Microsoft MVP since 2005
 DevelopMentor instructor
 Twitter: @mauricedb
 Blog: http://msmvps.com/blogs/theproblemsolver/
 Web: http://www.HTML5Support.nl
 E-mail: Maurice.de.Beijer@gmail.com

3. Agenda
 What is TypeScript?
 Why do we need TypeScript?
 What is wrong with JavaScript?
 TypeScript features
 Type annotations
 Type inference
 Modules
 Classes

4. What is TypeScript?
 An open source programming language developed at Microsoft
 By Anders Hejlsberg, lead architect of C#
 A super set of JavaScript
 All JavaScript is valid TypeScript
 Adds optional type checking, classes, interfaces and more
 Compiles to “normal” JavaScript
 Either ECMAScript 5 or ECMAScipt 3

5. Why do we need TypeScript?
 JavaScript was designed for small scripts
 These days JavaScript applications get bigger and more complex
 Gmail is reported to have 443,000 lines of JavaScript in 2010
 This trend will continue
 Single Page Applications in the browser
 Node.js on the server

6. What is wrong with JavaScript?

7. Douglas Crockford on TypeScript
Microsoft's TypeScript may be the best of the many JavaScript front ends. It seems to
generate the most attractive code. And I think it should take pressure off of the
ECMAScript Standard for new features like type declarations and classes. Anders has
shown that these can be provided nicely by a preprocessor, so there is no need to change
the underlying language.
I think that JavaScript's loose typing is one of its best features and that type checking is
way overrated. TypeScript adds sweetness, but at a price. It is not a price I am willing to
pay.

8. Things TypeScript adds to JavaScript
 Type annotations
 Type inference
 Modules
 Classes
 Interfaces
 Based on the ECMAScript 6 proposed standard

9. Type annotations

10. Type inference

11. Type annotations/arrays

12. Type annotations/param arrays

13. Arrow functions

14. Type annotations/casts

15. TypeScript type definitions
 The DOM and standard JavaScript types are provided

16. DefinitelyTyped

17. Modules

18. Interfaces

19. Interfaces

20. Interfaces & function overloading

21. Interfaces & type definitions

22. Classes

23. Classes & constructors

24. Classes & constructors

25. Classes & properties

26. Arrow functions revisited

27. Arrow functions revisited

28. Classes & inheritance

29. TypeScript is still JavaScript
 Not all JavaScript problems are solved by TypeScript
 Some older browsers support ECMAScript 3 (December 1999)
 Some older browsers have non standard DOM/CSS implementations
 jQuery remains an extremely useful library

30. Conclusion
 TypeScript is not perfect
 But it helps a lot
 You are not forced to use a new language
 Leverage existing JavaScript skills en libraries
 Consider it for your next “large“ JavaScript project
 After all the risk is small