Migrating Homepage from Django to React - reactjs

Question

i built a Homepage using the Django templating engine and on one page is a js application i wrote. Now i moved to a Frontend <-> Backend architecture with React and Django-rest-framework.
The Application i had in Django was served as a .html file with <script> tags for the js part.
Now i moved to React and i'm serving the html elements through a React component and through React-helmet i'm adding the <script> tags for this specific page. The actual .js files reside in the /public folder of react.
I thought i can replicate this way the old structure. But now i get Errors that the .js files can't import classes from the first external script.
What could be the difference in this setup ?
Django:
<script type="text/javascript" defer src="https://unpkg.com/quantum-circuit"></script>
<script defer src="{% static 'path/to/file.js' %}"></script>
...
React:
<script type="text/javascript" defer src="https://unpkg.com/quantum-circuit"></script>
<script defer src={process.env.PUBLIC_URL + 'path/to/file.js' }></script>
...
The Error Message at React is that my file.js can't find the import from the first <script>. But in Django there is no problem.
the import statement in file.js is:
import { QuantumCircuit } from "quantum-circuit";
Thank you in advance for every answer :)

Answer 1

It seems that the first external script is not ready when my custom scripts are trying to call it.
I fixed the issue using the useEffect hook. It calls the external script and if it's ready i'm calling my custom scripts.
Despite i was able to resolve this issue, i'm wondering why this hasn't happend in Django before.