How do I use a service?

Import the exported singleton const, not the class:

import { ThemeTogglerService } from '../../../services/index.js';

private _handleToggle(): void {
  ThemeTogglerService.toggleTheme();
}

Importing the class instead and calling new ThemeTogglerService() throws — see How do I create a service?.

Because every service method is auto-bound to its instance, methods can be destructured or passed directly as callbacks without losing this:

const { toggleTheme } = ThemeTogglerService;
button.addEventListener('click', toggleTheme); // works, `this` still correct

Any component, view, or other service can import and call a service's methods the same way — there's no special context required.