I don't know whether this has appeared obvious here. I would like to point out that as far as client-side (browser) JavaScript is concerned, you can add type="module" to both external as well as internal js scripts.
Say, you have a file 'module.js':
var a = 10;
export {a};
You can use it in an external script, in which you do the import, eg.:
<!DOCTYPE html><html><body>
<script type="module" src="test.js"></script><!-- Here use type="module" rather than type="text/javascript" -->
</body></html>
test.js:
import {a} from "./module.js";
alert(a);
You can also use it in an internal script, eg.:
<!DOCTYPE html><html><body>
<script type="module">
import {a} from "./module.js";
alert(a);
</script>
</body></html>
It is worthwhile mentioning that for relative paths, you must not omit the "./" characters, ie.:
import {a} from "module.js"; // this won't work