Why do you need the @ decorators for certain injectables in V2?

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1

@IRouter, @ILogger decorators needed to inject the logger and router in V2 what is the logic behind this?

2

These are the parameter decorators as well as injection tokens that registers the dependencies of a class (as metadata). When a class is instantiated via DI, these dependencies are fetched from the metadata and recursively resolved in order to instantiate the class.

3

Sure, but why are they needed when they were not in V1 with @autoInject useage.

4

The @autoinject is not yet ported to Au2. We might port that.

cc: @bigopon

5

Considering that every view class I have uses @autoinject, I consider @autoinject as a rather basic requirement if porting from v1

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6

Interface types do not exist in JavaScript, these decorators allow the DI container to inject the correct instance

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7

When using typescript, you don’t need to explicitly annotate the types (docs)

@autoinject is called @inject in Aurelia 2:

import { inject } from 'aurelia';

@inject()
export class FileImporter {
  constructor(private fileReader: FileReader, logger: Logger) { ... }
}
8

If they are real types

9

as a matter of fact it doesnt matter you use as long as anyone of the aurelia ones is provided the deco metadata for the class is provided and DI works.

As @MaximBalaganskiy mentioned though, property injectors make use of a special Symbol wrapping a TS interface and thus making it “materialized” aka not disappear after transpilation. for these you need to be explicit and use the given injection tokens.

10

as for the purpose, I recommend giving this great DI docs a thorough read Dependency injection (DI) - The Aurelia Docs where all what I mentioned before plus in the “using interfaces” section you get a nice rundown. it also goes into why you’d want to do that, e.g. a plugin providing overridable named configurations

11

Yes, of course, sorry for being inaccurate. I often use abstract classes instead of interfaces in cases where I need dependency injection.