Imperative Distribution

credit.md

After Ryosuke, Travis, Wilson, William, and I discussed the problem for an hour over a burrito, William came up with this approach. All hail William.

select.js

var shadow = host.createShadowRoot({
  mode: "closed",
  distribute: (distributionList, insertionList) => {
    for(var i = 0; i < distributionList.length; i++) {
      for(var ii = 0; ii < insertionList.length; ii++) {
        var select = insertionList[ii].getAttribute("select")
        if(select != null && distributionList[i].matches(select)) {
          insertionList[ii].add(distrubtionList[i])
        } else if(select == null) {
          insertionList[ii].add(distrubtionList[i])
        }
      }
    }
  }
})
host.shadowRoot.distribute()
// mutation observer code that invokes distribute() on childList changes

shadow.webidl

callback DistributionCallback = void (sequence<(Text or Element)>, sequence<HTMLContentElement>);
enum ShadowRootMode { "open", "closed" };
dictionary ShadowRootInit {
  require ShadowRootMode mode;
  require DistributionCallback distribute;
};
partial interface Element {
  ShadowRoot createShadowRoot(ShadowRootInit options);
};
partial interface ShadowRoot {
  void distribute(); // invoke the callback, recursively if there's nesting
};
interface HTMLContentElement : HTMLElement {
  void add((Text or Element) node);
};