Angular2/TypeScript: error TS2345: Argument of type 'String' is not assignable to parameter of type 'string'

I have the following code, which I am using to create a Casino Management System: ``` import { Component, OnInit } from '@angular/core'; import { Router } from '@angular/router'; import { Observable } from 'rxjs/Observable'; import { Subject } from 'rxjs/Subject'; import { SearchService } from './search.service'; import { Data } from './datatypings'; @Component({ moduleId: module.id, selector: 'casino-search', templateUrl: 'search.component.html', styleUrls: [ 'search.component.css' ], providers: [SearchService] }) export class SearchComponent implements OnInit { data: Observable<Data[]>; private searchTerms = new Subject<String>(); constructor( private searchService: SearchService, private router: Router) {} // Push a search term into the observable stream search(term: string): void { this.searchTerms.next(term); } ngOnInit(): void { this.data = this.searchTerms .debounceTime(150) // wait for 150ms pause in events .distinctUntilChanged() // ignore if next search term is same as previous .switchMap(term => term // switch to new observable each time // return the http search observable ? this.searchService.search(term) // or the observable of empty data if no search term : Observable.of<Data[]>([])) .catch(error => { // TODO: real error handling console.log(error); return Observable.of<Data[]>([]); }); } gotoDetail(data: Data): void { let link = ['/detail', data.id]; this.router.navigate(link); } } ``` However, when I attempt to transpile this code from TypeScript to JavaScript I get this error: ``` app/data/search.component.ts(37,37): error TS2345: Argument of type 'String' is not assignable to parameter of type 'string'. 'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible. ``` Now, I've fixed the error simply by changing `String` to `string` within the angle braces but I want to be able to proceed in future without creating similar errors, and also to write the best code I can... So I'm wondering if someone could clear this up for me: I think I understand that a parameter with a wrapper class is something which encapsulates a primitive class and provides some sort of additional, usually interfacing related, behaviour (correct me if I'm wrong here), and I see why it might then not be possible to assign the contents of what is essentially a broader declared variable type to the more simple primitive, there is another aspect of the error message which interests me, that is: Why would it be preferable to use type 'string' over type 'String' in Angular2/Typescript in such a general sense as the error seems to imply? What is it which makes this preferential?