be-evanescent

be-evanescent is a web component decorator that removes the element it adorns from the DOM tree when the web component definitions it monitors for become registered.

Size of package, including custom element behavior framework (be-decorated):

Size of new code in this package:

The biggest use case is providing initial css rules for light children, prior to being slotted. This is important for avoiding FOUC. But leaving the styles behind when no longer applicable, could have a lasting negative impact on other light children waiting for their web components to become registered, as well as non-shadowed content. Not to mention the performance impact of having non applicable css sitting in memory.

be-evanescent is an attribute-based alternative to transient-style.

Syntax

<be-hive>
    <script type=emc src="be-evanescent/emc.json"></script>
</be-hive>
<style be-evanescent='["my-component"]'>
    div{
        color: red;
    }
</style>
<div>hello</div>
<script>
    setTimeout(() => {
        customElements.define('my-component', class extends HTMLElement {} );
    }, 3000);
</script>

The style tag is removed from the DOM tree as soon as web component "be-evanescent" is registered.

Assuming the parent element name

If no custom element names are specified, but the style element being enhanced is within a light child region of a custom element, assume that is the only one to wait for:

<be-hive>
    <script type=emc src="be-evanescent/emc.json"></script>
</be-hive>
<my-component>
<style be-evanescent>
    div{
        color: red;
    }
</style>
<div>hello</div>
</my-component>
<script>
    setTimeout(() => {
        customElements.define('my-component', class extends HTMLElement {} );
    }, 3000);
</script>

Viewing Locally

Any web server that serves static files with server-side includes will do but...

1. Install git
2. Fork/clone this repo
3. Install node.js
4. Open command window to folder where you cloned this repo

5. git submodule add https://github.com/bahrus/types.git types

6. git submodule update --init --recursive

7. npm install

8. npm run serve

9. Open http://localhost:8000/demo/ in a modern browser

Using from CDN:

<script type=module crossorigin=anonymous>
    import 'https://esm.run/be-evanescent';
</script>