Access to Script at ' from origin 'null' has been blocked by CORS policy

ES6 modules are subject to same-origin policy. You need to run your script from a local server, opening the file directly with a browser will not work.

see here ES6 module support in Chrome 62/Chrome Canary 64, does not work locally, CORS error

Looks like you're trying to open the web-page locally (via file:// protocol) i.e. double clicking the .html file. Unfortunately modules only work via HTTP(s), so all you need to do is use a local web server. Popular choices include:

• Live Server, a VS Code extension that adds a right-click option to run your pages with a local server.

• Node static server, a simple http server to serve static resource files from a local directory.

• Node live server is easy to install and use:

  npm install -g live-server // Install globally via npm
  live-server                // Run in the html's directory