How do I implement systemjs in Angular 6+?

I'm trying to learn how to make plugins work in Angular, however after adding systemjs I get the following error:

Uncaught ReferenceError: SystemJS is not defined

I implemented systemjs like this:

import { System } from 'systemjs';
declare const SystemJS: System;

import * as angularCore from '@angular/core';
import * as angularCommon from '@angular/common';
import * as angularCommonHttp from '@angular/common/http';
import * as angularForms from '@angular/forms';
import * as angularAnimations from '@angular/animations';
import * as angularPlatformBrowser from '@angular/platform-browser';
import * as angularPlatformBrowserDynamic from '@angular/platform-browser-dynamic';

//error thrown here
SystemJS.set('@angular/core', SystemJS.newModule(angularCore));
SystemJS.set('@angular/common', SystemJS.newModule(angularCommon));
SystemJS.set('@angular/common/http', SystemJS.newModule(angularCommonHttp));
SystemJS.set('@angular/forms', SystemJS.newModule(angularForms));
SystemJS.set('@angular/animations', SystemJS.newModule(angularAnimations));
SystemJS.set('@angular/platform-browser', SystemJS.newModule(angularPlatformBrowser));
SystemJS.set('@angular/platform-browser-dynamic', SystemJS.newModule(angularPlatformBrowserDynamic));

SystemJS.config({ meta: { '*': { authorization: true } } });

What am I missing?

My code where I use systemjs: https://github.com/FrisoDenijs/angular-pluggable-architecture/blob/master/dashboard/src/app/dashboard/dashboard/dashboard.component.ts

My commit with attempted fixes: https://github.com/FrisoDenijs/pluggable-angular-example/commit/4472560da17b69c13809be931f6966d9254d10d1

The repo I use as example: https://github.com/paucls/angular-pluggable-architecture

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