Failed to resolve module specifier

If you're getting

Uncaught (in promise) TypeError: Failed to resolve module specifier 'modules/example.js'

… and the module path is relative, make sure it starts with a ./.

This will not work:

import("modules/example.js").then(function(Example) {
    window.Example = new Example.default;
});

This will:

//-------v
import("./modules/example.js").then(function(Example) {
    window.Example = new Example.default;
});