Angular / Typescript：编写从基类派生的工厂返回类型

Question

I'm trying to write a factory method that returns classes, like this:

getWidget<T extends WidgetBase>(componentName: string): Type<T> {
    switch (componentName) {
        default:
            throw new Error(`Widget ${componentName} is not registered in the system`);
        case "Widget2":
            return Widget2Component;
    }
}

where Widget2Component is a classe defined in another file (Angular component) which derives from WidgetBase, and abstract class, and Type<> is an Angular interface defined like this:

interface Type<T> extends Function {
    new (...args: any[]): T
}

The compiler complains:

Type 'typeof Widget2Component' is not assignable to type 'Type<T>' . Type 'Widget2Component' is not assignable to type 'T' .

but I don't get why... Widget2Component extends WidgetBase!

Answer 1

Titian is right in what he said in the comments... So I modified my method to this:

getWidget(componentName: string): Type<WidgetBase> {
    switch (componentName) {
        default:
            throw new Error(`Widget ${componentName} is not registered in the system`);
        case "Widget1":
            return Widget1Component;
        case "Widget2":
            return Widget2Component;
    }
}