The project I have been working on integrates with an external API. It requires a JavaScript reference to be added to the index.html file (i.e. a <script> element). The URL to this script changes, depending on the environment the application uses (local, dev, test, prod). I wanted to explore how to make this reference dynamically loaded via the environment configuration file.

Here’s how the index.html file looks now:

<!doctype html>
<html lang="en">
  <meta charset="utf-8">
  <base href="/">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <script src=""></script>

What I need to be able to do is add this URL to the environment.ts and files like this:

export const environment = {
  production: false,
  cdnUrl: ''

I found a great article describing how to accomplish this:

So I decided to give it a try.

The Script Service

I added a new service to my project using the Angular CLI:

ng g s core\script --skip-tests

I created a list of scripts I wanted to be load-able via the service. I could add more if I wished, just adding a new key/value pair giving each script a unique key.

import { environment } from '../../environments/environment';

const loadableScripts = [
  { name: 'cdn', src: environment.cdnUrl }

Then modified the service to track each script’s loaded status:

  private scripts: any = {};

  constructor() {
    loadableScripts.forEach((script: any) => {
      this.scripts[] = {
        loaded: false,
        src: script.src

And then added the loadScript method. I didn’t require the ‘load’ method so I left it out. Also, I didn’t require support for IE, so I just implement the non-IE approach using the onload event:

  // load the script
  loadScript(name: string): Promise<any>  {
    return new Promise((resolve, reject) => {
      // resolve if already loaded
      if (this.scripts[name].loaded) {
        resolve({script: name, loaded: true, status: 'Already Loaded'});
      } else {
        // load script
        const script = document.createElement('script');
        script.type = 'text/javascript';
        script.src = this.scripts[name].src;

        script.onload = () => {
          this.scripts[name].loaded = true;
          resolve({script: name, loaded: true, status: 'Loaded'});

        script.onerror = (error: any) => resolve({script: name, loaded: false, status: 'Loaded'});

        // finally append the script tag in the DOM

NOTE The IE support presented in the blog post didn’t seem to compile in Angular 10. It is possible it is only a TypeScript type issue and using any might correct the issue. Not sure, but if you are going to use it with IE, you are warned it may need some additional attention.

Using the Script Service

I injected the new script service into the component that required the CDN URL script. I set a boolean flag to let me know if the script was loaded.

  isCdnLoaded: boolean;

  constructor(private scriptService: ScriptService) {
    this.isCdnLoaded = false;

Then in the OnInit handler, I loaded my script:

    this.scriptService.loadScript('cdn').then(() => {
      this.isCdnLoaded = true;

The Results

When I loaded the application, I discovered that the script was not loaded. Or at least that is what I initially thought. But some quick console.log statements told me that the script was loading just fine. The issue was with timing. The script was being dynamically added to the DOM AFTER the template needed the script’s contents. So it ended up giving me a JavaScript error as if the script wasn’t loaded.

To work around this, I added an *ngIf to the element in the component that required the script:

<div *ngIf="isCdnLoaded">

This allowed the script time to load and once complete, would render the element(s) that require the functions within the script.

NOTE If I so desired I could swap out the use of Promises with RxJs Observables. I might do that in the future, but the use of promises for this sort of thing seems to fit quite nicely into my existing application.


I was glad to find someone willing to post a solution to the same sort of problem I was faced with. While it wasn’t a perfect match for my use case, it gave me enough to run with and get working in my context. Thanks Lukas!