What does the @ (at sign) mean in the latest TypeScript (presumably v1.5) example?

Question

There is a very interesting picture was posted in the official TypeScript blog.

I wonder what the @ (at sign) symbol is doing there since (as far as I know) it cannot be used in JavaScript identifiers.

Answer 1

The big news this week is the merging of AtScript and TypeScript.

The following example from the AtScript documentation...

@Component() class MyApp {   server:Server;   @Bind('name') name:string;   @Event('foo') fooFn:Function;   @Inject()   constructor(@parent server:Server) {}   greet():string {} } 

Compiles into the following JavaScript...

function MyApp() {} MyApp.properties = {   'server': { is: Server },   'name': { is:string,             annotate: [new Bind('name']},   'fooFn': { is:Function,              annotate:[new Event('foo')]} } MyApp.annotate = [   new Component(),   new Inject() ]; MyApp.parameters = [   {is:Server, annotate:[parent]} ]; MyApp.prototype.greet = function() {} MyApp.prototype.greet.returns = string; 

AtScript was planned to be a layer on top of TypeScript (i.e. a super-set of a super-set) - but now the two projects are one.

Annotations are described thus:

• AtScript annotation syntax is just a shorthand of placing the same information in ES5. It would be reasonable for an ES5 developer to write these annotations manually. A helper library could even be provided.

• Annotations can only be placed on functions.

• An annotation placed on a class is an annotation placed on the class’ constructor function.

• An annotation placed on a field gets moved to the constructor function.

• All annotations are translated as properties on a function.