Frequently Asked Questions

Why Don't Components Display with Self-Closing Tags?

mdui is a library based on Web Components. Web Components do not support self-closing tags, so you should always use closing tags with mdui components.

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How to Prevent Unstyled Components Display Before Loading?

mdui components are registered via JavaScript, which may cause a brief unstyled display until the JavaScript loads and registers the components. Here are two solutions:

One solution is to use the :defined pseudo-class to hide unregistered mdui components. The following CSS hides all unregistered mdui components and shows them once registered:

:not(:defined) {
  visibility: hidden;

Another solution is to use the customElements.whenDefined() method. This method returns a promise that resolves when the specified component is registered. To handle cases where some components may fail to load, use Promise.allSettled().

In the following example, the <body> element is initially hidden using opacity: 0 and fades in after the components are registered. Promise.allSettled() is used to wait for all promises to complete, ensuring the page displays properly even if a component fails to load.

  body {
    opacity: 0;

  body.ready {
    opacity: 1;
    transition: 0.25s opacity;

<script type="module">
  await Promise.allSettled([

  // After registering the button, card, and checkbox components, add the 'ready' class to fade in the page
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