Angular compilation encounters errors

While following a tutorial from Angular University, I encountered an issue where running ng serve/npm start would fail. However, simply re-saving any file by adding or removing a blank space would result in successful compilation. You can view the screenshot here.

My Package.json:

{
  "name": "reactive-patterns-course",
  "version": "0.0.0",
  "license": "MIT",
  "angular-cli": {},
  "scripts": {
    "ng": "ng",
    "start": "./node_modules/.bin/ng serve  --proxy-config proxy.conf.json",
    "rest-api": "./node_modules/.bin/ts-node ./src/server/server.ts",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    // List of dependencies
  },
  "devDependencies": {
    // List of dev dependencies
  }
}

Could someone assist with this issue? I tried running NPM update without success. My environment details are:
Angular CLI: 1.7.4
Node: 8.10.0

I am not using any generic types here. Even if someone were to use them, it should consistently fail. Below is the app-data file content:

import * as _ from 'lodash';
import {Observable} from 'rxjs/Observable';
import {Lesson} from '../shared/model/lesson';

// Definition of interfaces and classes

export let lessonList$: Observable = {
  subscribe: obs => lessonsListSubject.subscribe(obs),
  unsubscribe: obs => lessonsListSubject.unsubscribe(obs)

};

let lessons: Lesson[] = [];

export function initializeLessonsList(newList: Lesson[]) {
  // Function implementation
}

Answer №1

It's clear from the error message provided (including the file and line number - app-data.ts(15,37)) that Observable is a generic type and must have one specified type. Therefore, assigning an undefined type like someVar: Observable is invalid.

To fix this issue in your code, replace

export let lessonList$: Observable = {
with
export let lessonList$: Observable<any> = {
or define a specific type for the Observable to stream.

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