Angular 7 error RangeError: Maximum call stack size exceeded

1.This error occur when there is an infinite loop.
As you have mentioned that the page loads when app-heroes is commented, this might be used as selector-name for more than one component which is not allowed.
This can cause an infinite loop and fail to load components.

2. Try making below edits,

hero.component.html

<ul class="heroes">
  <li *ngFor="let hero of heroes" (click)="onSelect(hero)" [class.selected]="hero === selectedHero">
    <span class="badge">{{hero.id}}</span> {{hero.name}}
  </li>
</ul>

<app-hero-detail [hero]="selectedhero"></app-hero-detail> 

hero.detail.component.html

<div *ngIf="hero">
  <h2>{{hero.name}} Details</h2>
  <div><span>id: </span>{{hero.id}}</div>
  <div>
    <label>name:
      <input [(ngModel)]="hero.name" placeholder="name"/>
    </label>
  </div>
</div>

Hope this helps.