Establishing a typescript class as an interface

While attempting to upgrade to TypeScript 3.5, I ran into an issue with a signature that has been overlooked by the ts-compiler, despite being present for years.

A third-party framework (knockoutJS) requires me to pass something that adheres to this:

interface ViewModelFunction {
    (params?: any): any;
}

Interestingly, at runtime, it seems to work by implementing something like this:

class MyClass {
  public foobar: string;
  constructor(params: { foo: string; bar: number }) {
    this.foobar = params.foo + params.bar;
  }
  public doSomething = () => {
    return this.foobar.length;
  }
}

and then passing MyClass into a function that expects ViewModelFunction as an attribute. Despite the code functioning correctly, this appears to be primarily a TypeScript problem. For some reason, TypeScript 3.5 suddenly recognizes this discrepancy, while previous versions did not allow syntax like:

class MyClass implements ViewModelFunction{...}

Is there a way to convert the Class into the ViewModelFunction interface?

Answer №1

let createViewModel: ViewModelFunction = parameters => new CustomClass(parameters);

Answer №2

To streamline your code, consider moving the functions doSomething and public method foobar to an interface. This interface can then be implemented by objects that also implement the ViewModelFunction.

interface ViewModelFunction {
  (params?: any): any;
}

interface MyClass {
  foobar: string;
  doSomething(): number;
}

interface MyF extends MyClass, ViewModelFunction {}

function createMyFInstance(foobar: string): MyF {
  const instance = () => {yourViewModel();};
  instance.foobar = foobar;
  instance.doSomething = () => foobar.length;
  return instance;
}

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