How to load custom script in react?

This is somewhat similar to this question:

Adding script tag to React/JSX

But in my case I am loading a script like this:

<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
})(window,document,'script','dataLayer','ID');</script>
<!-- End Google Tag Manager -->

Now I know there is a npm package for the google tag manager but I am curious if I would like to do this in a custom way how would I go about?

In the above question I see a lot of:

const script = document.createElement("script");

script.src = "https://use.typekit.net/foobar.js";
script.async = true;

document.body.appendChild(script);

Which is fine but if I have a function inside of the loaded script how would I go about executing this correctly?

from How to load custom script in react?