once-defined

A minimalistic, ~140 bytes, boilerplate to wait for Custom Elements, or libraries, definition.

import when from 'once-defined';
// const when = require('once-defined');
// <script src="//unpkg.com/once-defined">

// other custom elements
when(['outer-comp', 'inner-comp']).then(([Outer, Inner]) => {
  // define your components when Outer or Inner classes
  // have been registered
});

// uce library example / single name
when('uce-lib').then(({define, render, html, svg, css}) => {
  // define your components
});

If the awaited component/library is just one entry, it's returned right away. If it's a list of entries, each entry will be found in its related index.

Why

The standard decided that once you customElements.whenDefined(tagName) you need to customElements.get(tagName) once the initial, explicit, intent to wait/retrieve it, is resolved, as specs don't return what you were waiting for once resolved.

With this module, that weights nothing, you can forget about the following boilerplate:

customElements
  .whenDefined(thing)
  .then(() => customElements.get(thing))
  .then(thing => {
    console.log('finally we have', thing);
  });

Use just when(thing).then(thing => { ... }) and call it a day 🎉