Function registerDestroyHooksIfSupported

packages/core/src/render3/di_setup.ts:254–290

* Registers the `ngOnDestroy` hook of a provider, if the provider supports destroy hooks. * @param tView `TView` in which to register the hook. * @param provider Provider whose hook should be registered. * @param contextIndex Index under which to find the context for the hook when it's being invo

(
  tView: TView,
  provider: Exclude<Provider, any[]>,
  contextIndex: number,
  indexInFactory?: number,
)

 * provider factory.
 */
function registerDestroyHooksIfSupported(
  tView: TView,
  provider: Exclude<Provider, any[]>,
  contextIndex: number,
  indexInFactory?: number,
) {
  const providerIsTypeProvider = isTypeProvider(provider);
  const providerIsClassProvider = isClassProvider(provider);

  if (providerIsTypeProvider || providerIsClassProvider) {
    // Resolve forward references as `useClass` can hold a forward reference.
    const classToken = providerIsClassProvider ? resolveForwardRef(provider.useClass) : provider;
    const prototype = classToken.prototype;
    const ngOnDestroy = prototype.ngOnDestroy;

    if (ngOnDestroy) {
      const hooks = tView.destroyHooks || (tView.destroyHooks = []);

      if (!providerIsTypeProvider && (provider as ClassProvider).multi) {
        ngDevMode &&
          assertDefined(
            indexInFactory,
            'indexInFactory when registering multi factory destroy hook',
          );
        const existingCallbacksIndex = hooks.indexOf(contextIndex);

        if (existingCallbacksIndex === -1) {
          hooks.push(contextIndex, [indexInFactory, ngOnDestroy]);
        } else {
          (hooks[existingCallbacksIndex + 1] as DestroyHookData).push(indexInFactory!, ngOnDestroy);
        }
      } else {
        hooks.push(contextIndex, ngOnDestroy);
      }
    }
  }
}

/**
 * Add a factory in a multi factory.