What is the method for returning a dynamically typed object in Typescript / Angular2?

I am currently working on developing a modal generator service that will be used to create different types of modals.

One issue I am facing is with the syntax in the function declaration. The current code looks like this:

private createModalComponent (compType : Type<Component>, vCref: ViewContainerRef): ComponentRef<compType> { ... }

However, this is resulting in an error stating "cannot find name 'compType'". I then attempted a more generic approach:

private createModalComponent<T> (compType : T, vCref: ViewContainerRef): ComponentRef<T> { ... }

But this led to an error saying "Argument of type 'T' is not assignable to parameter of type 'Type<{}>'. So now I'm stuck on how to return a dynamically typed object in TypeScript.

import { Injectable, ViewChild, ViewContainerRef, ElementRef,
         EventEmitter, OnInit, ComponentRef, ComponentFactoryResolver,
         Type, ReflectiveInjector } from '@angular/core';
import { WizardModalComponent } from './wizard-modal/wizard-modal.component'


@Injectable()
export class ModalGeneratorService {

  constructor(private _cmpFctryRslvr: ComponentFactoryResolver, private _vcRef: ViewContainerRef) {}

  private createModalComponent (compType : Type<Component>, vCref: ViewContainerRef): ComponentRef<compType> {
    let factory = this._cmpFctryRslvr.resolveComponentFactory(compType);
    // vCref is needed cause of that injector..
    let injector = ReflectiveInjector.fromResolvedProviders([], vCref.parentInjector);
    // create component without adding it directly to the DOM
    let comp = factory.create(injector);
    return comp;
  }

  createWizardModalcomponent(vCref : ViewContainerRef) {
    createModalComponent(WizardModalComponent, vCref);
  }
}

Answer №1

It's a bit unclear to me what the exact issue is, but here's a potential solution that could resolve it:

function createDynamicComponent<T extends Type<{}>> (compType : T, vCref: ViewContainerRef): ComponentRef<T> { ... }

In this code snippet, you're defining a generic function that takes a component type parameter constrained to either be or extend the `Type<{}>` type, which addresses the error message you encountered.

Answer №2

Here is a potential solution that I found:

Upon examining the ComponentFactory file within the angular 2 framework, I noticed that it utilizes the "any" type. However, as I delved deeper, I discovered the declaration of the create function with "<C>" included:

create(injector: Injector, projectableNodes?: any[][], rootSelectorOrNode?: string|any) : ComponentRef<C>

https://angular.io/docs/ts/latest/api/core/index/ComponentFactory-class.html

Answer №3

Big shoutout to all the amazing individuals who took the time to comment or provide an answer. I stumbled upon a solution that fits my needs perfectly and it's surprisingly simple.

All I had to do was utilize the 'any' type instead of the component type for the component reference, like this:

private createModalComponent (compType : Type<Component>, vCref: ViewContainerRef): ComponentRef<any> { ... }

During moments like these, it's important to remember that although Typescript predominantly relies on static typing, it graciously offers us the 'any' keyword as a lifeline. Hopefully, someone else will benefit from this insight as well.

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