创建扩展基类的所有类的实例

Question

I have a base class called Editor , I then have items that will extend that class. Is it possible for me to create an instance of all those classes that extend Editor without manually creating them all?

class Editor<T> {

}

class TransformEditor extends Editor<Transform> {

}

class SomethingEditor extends Editor<Something> {

}

So, in this example the code doesn't know TransformEditor exits, but it is in the codebase, so is it possible to do something where I can get a list of these items, then create an instance of each?

Answer 1

You can wrap all of these classes in a namespace and then you can iterate all of the exported items.
You can then check for each exported item if it is an instance of the Editor constructor.

Something like this:

namespace editors {
    export function getEditorClasses(): EditorConstructor<any>[] {
        let list = [];

        Object.keys(this).forEach(name => {
            let obj = this[name];

            if (obj.prototype instanceof editors.Editor) {
                list.push(obj);
            }
        });

        return list;
    }

    export interface EditorConstructor<T> {
        new(): Editor<T>;
    }

    export class Editor<T> {}

    export class TransformEditor extends Editor<string> {}

    export class SomethingEditor extends Editor<boolean> {}
}

console.log(editors.getEditorClasses()); // [function TransformEditor(), function SomethingEditor()]

( code in playground )

Answer 2

So there's no way to do this at runtime with TypeScript without adding additional code since there's no way to do this with JavaScript.

You could use TypeScript's decorators to track the children. Here's an extremely simple example:

class Editor {}

const children = []; // This could be an object that maps parents to children

function TrackChild(constructor: Function) {
  // You could also add more fancy prototype/constructor shenanigans here
  children.push(constructor);
}

@TrackChild 
class TransformEditor extends Editor {}

@TrackChild
class SomethingEditor extends Editor {}

console.log(children);

This decorator could of course become much more sophisticated. Here's a very detailed example of tracking a full genealogy with decorators