I have a thousands of this error after initial implementation nad typing in terminal ng serve my-app of and i can't resolve it. This is first time for me when i have problem like this inside angular with typescript Errors looks like this:

ERROR in ../../node_modules/@angular/flex-layout/core/typings/base/base2.d.ts:24:19 - error TS1086: An accessor cannot be declared in an ambient context.

24     protected get parentElement(): HTMLElement | null;
                     ~~~~~~~~~~~~~
../../node_modules/@angular/flex-layout/core/typings/base/base2.d.ts:26:19

- error TS1086: An accessor cannot be declared in an ambient context.

26     protected get nativeElement(): HTMLElement;
                     ~~~~~~~~~~~~~
../../node_modules/@angular/flex-layout/core/typings/base/base2.d.ts:28:9

- error TS1086: An accessor cannot be declared in an ambient context.

28     get activatedValue(): string;
           ~~~~~~~~~~~~~~
../../node_modules/@angular/flex-layout/core/typings/base/base2.d.ts:29:9

- error TS1086: An accessor cannot be declared in an ambient context.

29     set activatedValue(value: string);
           ~~~~~~~~~~~~~~
../../node_modules/@angular/flex-layout/core/typings/breakpoints/break-point-registry.d.ts:20:9

- error TS1086: An accessor cannot be declared in an ambient context. [...]

Does somebody know a reason? I can't test my app until I fix it.

Update 1

Okay, i make it forward. Most of errors is gone, but i have few ones now, for example first of them:

ERROR in src/app/main/main.component.ts:143:63 - error TS2322: Type 'string | undefined' is not assignable to type 'string'. Type 'undefined' is not assignable to type 'string'.

143 this.fileService.add({ isFolder: true, name: folder.name, parent: this.currentRoot ? this.currentRoot.id : 'root' });

Code looks like this:

main.component.ts:

currentRoot: MpFileElement = new MpFileElement();
...
    addFolder(folder: { name: string }) {
        this.fileService.add({ isFolder: true, name: folder.name, parent: 
    this.currentRoot ? this.currentRoot.id : 'root' });
        this.updateFileElementQuery();
    }
...

file.service.ts:

import { Injectable } from '@angular/core';

import { v4 } from 'uuid';
import { MpFileElement } from '../models/mp-file-element.model';
import { Observable } from 'rxjs/internal/Observable';
import { BehaviorSubject } from 'rxjs';

export interface IFileService {
    add(fileElement: MpFileElement);
    delete(id: string);
    update(id: string, update: Partial<MpFileElement>);
    queryInFolder(folderId: string): Observable<MpFileElement[]>;
    get(id: string): MpFileElement;
}

@Injectable()
export class MpFileService implements IFileService {

    constructor() {}
    private map = new Map<string, MpFileElement>()

    private querySubject: BehaviorSubject<MpFileElement[]>;

    add(fileElement: MpFileElement) {
        fileElement.id = v4();
        this.map.set(fileElement.id, this.clone(fileElement));
        return fileElement;
    }

    delete(id: string) {
        this.map.delete(id);
    }

    update(id: string, update: Partial<MpFileElement>) {
        let element = this.map.get(id);
        element = Object.assign(element, update);
        this.map.set(element.id, element);
    }
    queryInFolder(folderId: string) {
        const result: MpFileElement[] = [];
        this.map.forEach(element => {
            if (element.parent === folderId) {
                result.push(this.clone(element));
            }
        })
        if (!this.querySubject) {
            this.querySubject = new BehaviorSubject(result);
        } else {
            this.querySubject.next(result);
        }
        return this.querySubject.asObservable();
    }

    get(id: string) {
        return this.map.get(id);
    }

    clone(element: MpFileElement) {
        return JSON.parse(JSON.stringify(element));
    }
}