resolver.ts

import { Injectable } from '@angular/core';
import { 
  Resolve,
  ActivatedRouteSnapshot, 
  RouterStateSnapshot } from '@angular/router';
import { Post } from './post.model';
import { HttpClient } from '@angular/common/http';

@Injectable({
  providedIn: 'root'
})
export class PostResolverService implements Resolve<Post> {
  constructor(private http:HttpClient) { }
  
  async resolve(route: ActivatedRouteSnapshot) {
    const id = route.paramMap.get('id');
    const post = await this.http.get<Post>(`/assets/posts/${id}.json`).toPromise();
    return new Post(post.title, post.content);
  }
}