Can ng-content be utilized within the app-root component?

I have successfully developed an Angular application, and now I am looking to integrate it with a content management system that generates static pages. In order to achieve this, I need to utilize content projection from the main index.html file.

The desired structure would look like this:

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>AngularCMS</title>
    <base href="/">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="icon" type="image/x-icon" href="favicon.ico">
  </head>
  <body>
    <app-root>Content injected from index.html</app-root>
  </body>
</html>

Next, the app-root component can implement content projection by including

<ng-content></ng-content>
in its template:

@Component({
  selector: 'app-root',
  template: '<p>External Content Projection:<ng-content></ng-content></p>',
  styleUrls: ['./app.component.css']
})
export class AppComponent { }

However, when trying this out, the result does not match the expected output. The rendered text ends up being:

  • External Content Projection:1111

This leads me to my question:

  • Is it feasible to apply content projection from outside the Angular application, similar to the example shared above?
  • If yes, then how can this be achieved? If no, what are the limitations?

Edit: Some may wonder about the purpose behind such integration. To provide some context: my Angular app includes customizable components for financial back-testing simulations. This involves fetching historical data, running tests, and displaying results graphically. I aim to showcase these simulations on platforms like WordPress, Dokuwiki, or even as static pages served by Apache. Here's a theoretical scenario:

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Example Buy &amp; Hold Strategy</title>
    <base href="./">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="icon" type="image/x-icon" href="favicon.ico">
  </head>
  <body>
    <p>This simulation demonstrates a pure <em>Buy &amp; Hold</em> strategy, investing $100,001 in the S&amp;P500 from January 1, 2000, to January 1, 2020:</p>
    <app-root>
      <simulation start="2000-01-01" end="2020-4-9" quotes="SPY">
        <chart-report>
          <chart-report-configuration show="SPY.CLOSE" showDataAs="LINE" showDataOn="LEFT" normalize="true"></chart-report-configuration>
          <chart-report-configuration show="BAH.NAV" showDataAs="LINE" showDataOn="LEFT" normalize="true"></chart-report-configuration>
        </chart-report>
        <accounts>
          <swiss-quote id="BAH" cash="100000">
            <strategy>
              <buy-and-hold assetName="SPY"></buy-and-hold>
            </strategy>
          </swiss-quote>
        </accounts>
      </simulation>
    </app-root>
    <p/>Additional information goes here.</p>
  </body>
</html>

Answer №1

At the moment, Angular up to version 15 does not support injecting app-root content with ng-content. However, this feature is currently under consideration and there is an ongoing issue discussing it in more detail: https://github.com/angular/angular/issues/4946


One approach I've taken to display the Initial Loading Indicator is by initially placing the default app-root content outside the app-root element and then projecting it into the app component.

In index.html:

...
<body>
  <div id="initialization-container">
    Initializing...
  </div>
  <app-root></app-root>
</body>
...

In app.component.html:

<ng-container *ngIf="isInitializing$ | async; else appInitialized">
  <app-initialization-container/>
</ng-container>

<ng-template #appInitialized>
  APPLICATION
</ng-template>

In initialization-container.ts:

import {AfterViewInit, ChangeDetectionStrategy, Component, ElementRef, Renderer2} from '@angular/core';

@Component({
  selector: 'app-initialization-container',
  template: '',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class InitializationContainerComponent implements AfterViewInit {
  constructor(
    private render: Renderer2,
    private hostRef: ElementRef
  ) {
  }

  ngAfterViewInit() {
    const el = document.getElementById('initialization-container');
    if (el != null) {
      this.render.appendChild(this.hostRef.nativeElement, el);
    }
  }
}

Another option for handling the loading indicator scenario could be removing it from the DOM once the loading is complete. However, this example showcases how to project content into the application to suit your specific use-case.

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