global window properties are not loaded when loading an external script

🐛 bug report

Description of the problem

When loading external script, some global window properties should be added.
Specifically, after loading 'mocha' and 'chai' scripts, the following properties should exist: 'window.mocha' and 'window.chai'.
This works well in a normal environment.
However, when running the same code in a codesandbox, these properties are missing from the global 'window' variable.

It seems that the chai.js and mocha.js script files are downloaded (in the network tab of the browser debugger).

I isolated the problem to the location of 'index.html' file. When it is under the 'src' folder, this problem persists.
When it is under the project root folder, this problem doesn't occur.

How has this issue affected you? What are you trying to accomplish?

My goal is to create a codesandbox to demonstrate Mocha capability of running in a browser, as specified here:
https://mochajs.org/#running-mocha-in-the-browser

To Reproduce

Create a Node environment with a simple html, sourcing the following script:

<script src="https://unpkg.com/chai/chai.js"></script>

Then, in another script, try to access window.chai

In a non-codesandbox environment, you will get a structure.
In codesandbox, you will get undefined.

So, when trying to access window.chai.expect, the following Type Error occurs:

Cannot read properties of undefined (reading 'expect')

The reason is that chai is undefined in window

Link to sandbox:

link to sandbox

Your Environment

Start by reproducing the linked sandbox with index.html under src, then compare its external-script loading with index.html at the project root. Trace why chai.js and mocha.js do not populate window and verify that window.chai and window.mocha are available after loading.