be-a-beacon

be-a-beacon is an HTML Element enhancement that causes the HTMLTemplate (or any other) element it adorns to emit bubbling event 'i-am-here", the moment it is connected to the live DOM tree. It is important to note that be-a-beacon is a special type of custom enhancement -- one that only should be activated in the live DOM tree, not during template instantiation. During template instantiation, we already know everything that is in the template via simple css queries -- it is a closed system. be-a-beacon is specifically tailored for situations where elements arrive on the scene unexpectedly -- while the server-rendered HTML is streaming, or when fragments are added when conditions are warranted in the browser (i.e. lazy loading).

<div be-a-beacon>
    ...
</div>

Spell out the name of the event

To specify a different event name, set the attribute to the name ("type") of the event you would like it to emit:

<section>
    ...
    <div be-a-beacon=last-div-at-your-service>
        ...
    </div>
</section>

oSection.addEventListener('last-div-at-your-service', e => {
    console.log(e.target);
})

Announce the presence of the id of the element

This is useful, for example, for bundling HTML includes

<section>
    ...
    <template id=b0735b7a-84d1-42e9-b3b8-e24cb88f5985 be-a-beacon=#>
        ...
    </template>
</section>

So the special value of "#" means emit event with the name specified by the id.

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

Size of new code in this package:

Use cases

1. be-a-beacon provides a similar, but slightly different solution to a current limitation of the platform -- we don't know when a DOM element has finished parsing. The solution this component provides is an alternative to the solution spelled out here.

The difference is that this solution doesn't require a separate web component, but can simply "enhance" the last DOM element of the stream. The template element might be a good element to use be-a-beacon on, because the template element can be used universally -- it is one of the few elements that can appear in many more places without violating HTML decorum. In particular, it can appear inside a table element without being rudely ejected:

<table>
    <thead>
        ...
    </thead>
    <tbody>
        ...
    </tbody>
    <template be-a-beacon></template>
</table>

However, be-a-beacon can adorn any element, not just the template element. If adorning a custom element, you will need to prefix the attribute with "enh-by":

<my-fragment>
    ...
    <my-custom-element enh-by-be-a-beacon></my-custom-element>
</my-fragment>

2. If a div element (say) is populated by a (streaming) fetch request, and that populating is done numerous times based on user interaction / timing events, then the placement of the beacon at the end of the stream can be used instead of a mutation observer to indicate, for example, that some content that should be derived from the contents of the DOM is ready to be generated.

3. If a component wishes to provide its own default light children, in the event that the consumer doesn't provide their own, a cue is needed to know when no light children will be provided.

Viewing Locally

Any web server that serves static files (html, css, js) will do but...

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

5. npm install

6. npm run serve

7. Open http://localhost:3030/demo/dev in a modern browser.

Importing in ES Modules:

import 'be-a-beacon/be-a-beacon.js';

Using from CDN:

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