TypeError while instanciating generic Object

Question

I´m getting a TypeError: type is not a constructor while trying to transform API-Data to Frontend-Dtos.

The Transform-Method looks like this:

transform<T>(entities: any[]) {
    const tableDtos = new Array<T>();
    for (const entity of entities) {
      const dto: T = this.factory.createEntity(entity);
      tableDtos.push(dto);
    }
    return tableDtos;
  }

My Factory like this:

export class Factory {
  create<T>(type: (new () => T)): T {
    return new type();
  }
}

I took the solution from here . What am I missing here?

DTO

import { Entity} from 'src/models/api/Entity';

export class EntityTableEntry {

  id: number;
  name: string;

  constructor(entity: Entity) {
    this.id = entity.ID;
    this.name = entity.Name;
  }
}

Entity

export interface Cost {
  ID: number;
  Name: string;
  Description: string;
  Value: number;
}

The reason why I want to have an generic method is, that I would need to re-write the transform method for each API-Call, which is a complete mess!

Answer 1

I am assuming entities contains the data for the objects you want to create. As such it will not be callable with new . You want to pass in the actual class you want to create (maybe assign the data to the new instance):

class xx {
  factory: Factory = new Factory();
  transform<T>(type: (new () => T), entities: any[]) {
    const tableDtos = new Array<T>();
    for (const entity of entities) {
      const dto: T = this.factory.createEntity(type, entity);
      tableDtos.push(dto);
    }
    return tableDtos;
  }
}

class Factory {
  createEntity<T>(type: (new () => T), data: any): T {
    var r = new type();
    Object.assign(r, data) // guessing a decent implementation here 
    return r;
  }
}

class DataClass { a!: number }

var r = new xx().transform(DataClass, [{ a: 1 }]);
console.log(r);

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