Add "indexed properties"

[dmitryDemchenko]

In our project we use ActiveX objects accessible from JavaScript. I have .d.ts of COM library.
One of the external types has "indexed properties". As for now, it's TS declaration loks like

interface axType {
  Values(index:string):string;
}

JS code like

axObject.Values('F1') = 'test'

works just fine in runtime, but TS compiler shows the message: "Invalid left-hand side of assignment expression".

I can't see the way how to define that interface in .d.ts.

As I can imagine, it should be something like

class axType { 
  get Values(index:string): string 
  {
  //....
  }

  set Values(index:string, value: string)
  {
  // ...
  }
}

[RyanCavanaugh]

This is already supported. Use an index signature:

interface axType {
  Values: { [index: string]: string };
}

[zspitz]

@RyanCavanaugh Can I define a signature with multiple parameters? Or with types other than number or string?

[zspitz]

@RyanCavanaugh Also, won't defining the indexers this way require the use of square brackets:

axObject.Values['F1'] = 'test';

but the OP's Javascript uses invocation:

axObject.Values('F1') = 'test'

This seems to be a valid (although relatively unusual) pattern in ActiveX libraries, e.g. Item property on Scripting.Dictionary:

var d = new ActiveXObject("Scripting.Dictionary");
d.Item("a") = "Athens";

[dmitryDemchenko]

@zspitz as far as I can see JScript indexer is something not supported in ECMA; also TypeScript is intended to compile to JavaScript (ecma). That's why this kind of indexes definitely will not be supported in TypeScript.

In my project I ended up rewriting all calls like

d.Item("a") = "Athens"

into

AssignIndexedProperty(d, "a", " "Athens"")

and defining function

AssignIndexedProperty = new Function (d, name, value, "d(name) = value")

That trick worked good in JScript interpreter, but had terrible readability ((((

[zspitz]

@dmitryDemchenko You may be interested to know that I've written a tool to convert type libraries to Typescript definition files. https://github.com/zspitz/ts-activex-gen

[dmitryDemchenko]

@zspitz Nice job! I did almost the same for our ActiveX libraries, or, to be more accurate, for .NET "interop" libraries. It was very similar, but I suppose a little bit easier thanks to "reflection" mechanism.

[zspitz]

@dmitryDemchenko I originally was using .NET reflection, but there were too many mismatches between the .NET reflection model and the COM object model. I am currently using tlbinf32.dll.