When you say "Web Components", what is it that you are talking about? I assume you mean custom elements. Custom elements are DOM Nodes like any other. They are

When you say "Web Components", what is it that you are talking about? I assume you mean custom elements. Custom elements are DOM Nodes like any other. They are represented in JavaScript like any other object. Of course you can pass non-strings to DOM elements. Open your development console and type document.createElement('div').user = {name: 'Dmitri'}. Did you get an error?