TypeScript: how to extract the generic parameter from a type?

Question

Say I have a type like React.ComponentClass and I want to reference the Props part but it is unnamed in my current context.

To

Answer 1

Thought I'd share a real world example to extract the R generic type for MatDialogRef which is Angular material's dialog box.

I often have components like this, where the output 'model' is a simple interface that isn't quite worthy of its own named type.

export class DialogPleaseWaitComponent implements OnInit {

  constructor(@Inject(MAT_DIALOG_DATA) public data: DialogPleaseWaitModel,
              public dialogRef: MatDialogRef) { 

  }

So I came up with:

extractMatDialogResponse

I made it work in two 'modes', either taking the component type or the MatDialogRef itself. So I can put extractMatDialogResponse and get back { timedOut: boolean } :-)

Yes - if T is the component type then it requires dialogRef to be the exact name of the property, and it does need to be public.

type extractMatDialogResponse | { dialogRef: MatDialogRef }> = 
     T extends MatDialogRef ? R :                                                                                                          
     T extends { dialogRef: MatDialogRef } ? R : never;

Also yes this is the same mechanism as used by Xiv, but demonstrates how to make a 'targeted' extractor for a specific use.