Strange problem with AU1, inheritance, DialogService and dumber


My setup is Aurelia 1 + TypeScript + dumber.

I am encountering a strange problem with this (simplified) setup which involves class inheritance and DialogService.

In short:

  • base component which opens a dialog using its class as the viewModel
  • two derived components
  • page which requires both components

At runtime, the page breaks with the following error:


TypeError: Class extends value undefined is not a constructor or null


TypeError: class heritage inspectionAnswerListBase_1.InspectionAnswerListBase is not an object or null

What happens is that the first component works correctly, but in the second one the base class is undefined. Note that this is not dependent on the actual components but only in their order (the first works, the second breaks).
However, specifying the viewModel for the dialog as a module path (string) instead of an import DOES work.

Out tsconfig.json is:

  "compileOnSave": false,
  "compilerOptions": {
    "rootDir": "src/",
    "sourceMap": true,
    "target": "ES2017",
    "module": "AMD",
    "declaration": false,
    "removeComments": true,
    "importHelpers": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "noEmitOnError": true,
    "forceConsistentCasingInFileNames": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "alwaysStrict": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitAny": false,
    "noImplicitOverride": true
  "exclude": [

I do not seem to be able to pinpoint the exact source of the problem, I suspect some odd edge case.
I am not even sure whether I should expect a solution, but maybe something here rings a bell for someone.