CORS error referencing JavaScript files

Using this method to upload a Javascript file

But then, when I try to reference it from the Squarespace site, I get a CORS error:

Am I doing something wrong here?

Hi. I'm having this exact same issue-- both with Javascript files and trying to refer to a json file.   Were you able to find a solution?

I found a way to deal with it-- I put .js and .json files in a s3 bucket and turned out a CORS policy on the s3 bucket.

There's a fix that @dmitrykiselyov has used a few times as a way to give the browser what it needs.
I'll let him share it here if he chooses to. (He can also explain it better than me!) 

Hi @popsovy,

Try this path /s/runtime-es2015.js

<script src="/s/runtime-es2015.js"></script>

That's presumably what @popsovy was already doing, as it's the method used in the page he linked to. Unfortunately that doesn't work, as /s/filename.ext is loaded from static1.squarespace.com, for which Squarespace unhelpfully don't have a CORS Access-Control-Allow-Origin header.

Okay, so the correct answer seems to be to use the redirect URL (e.g. https://static1.squarespace.com/static/57014b5b746fb963478e3d4f/t/5d7ba83d4e25b616833d896b/1568385085375/runtime-es2015.js in @popsovy's case), not the path that @dmitrykiselyov mentioned.

How does one get/find the static1.squarespace.com URL @MattB2? Whenever I put in the domain.com/s/script.js URL into my browser, for example, it just automatically downloads the script file. Doesn't actually show where the redirect URL is.

Hi @popsovy - did you resolve this? 

Ccing you as well @MattB2

I am trying to use d3.csv to access a file I have uploaded as a link and whatever I get a 404 with the filename and a CORS with /s/ + filename or the full https static1.squarespace link...  Confused!