Use the connectedCallback function instead of a constructor.

For Custom Elements, the constructor method can be a little unwieldy to use; it is called as soon as the class is instantiated with document.createElement which will be before the element has been appended to the DOM. It can be simpler to put code within the connectedCallback which is fired when the element has been appended into the DOM.

https://github.com/github/eslint-plugin-custom-elements/blob/main/docs/rules/no-constructor.md