3js not recognized when within script file

I am trying to install the latest version of 3js.

I go by the directions on the 3js website, here:
https://threejs.org/docs/index.html#manual/en/introduction/Installation
I am doing part: “Install from CDN or static hosting”.

I have downloaded the library onto my computer, so I am referring to my own file there.

Using this, I can run 3js code.

But the problem is, if I try to run that given code in it’s own file, like this:

<script src="./thecode.js"></script>

I get error:
Uncaught ReferenceError: THREE is not defined

It is like it’s not recognizing threejs at all, in that file.
But it recognises threejs, if I just keep it in the index.html.
But I can’t just be programming in the index file forever.

How do I get it to recognize threejs in the file?

I have also tried adding type=“module”, to the reference, to no avail.