lite-signal.html

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<link rel="import" href="../polymer/polymer-element.html">

<script>
  (function() {
    // private list of subscribers
    var subscribers = []

    function getNewSignal(name, data) {
      // convert generic-signal event to named-signal event
      return new CustomEvent('lite-signal-' + name, {
        // if subscribers bubble, it's easy to get confusing duplicates
        // (1) listen on a container on behalf of local child
        // (2) some deep child ignores the event and it bubbles
        //     up to said container
        // (3) local child event bubbles up to container
        // also, for performance, we avoid subscribers flying up the
        // tree from all over the place
        bubbles: false,
        detail: data,
      });
    }

    // signal dispatcher
    function notify(name, data) {
      // dispatch named-signal to all 'subscribers' instances,
      // only interested listeners will react
      subscribers.forEach(function(sub) {
        // Generate a new CustomEvent for each instance:
        // Once an event is consumed, for some reason in FF it does not trigger anything in another subscriber
        // listening on the same event (https://github.com/ernsheong/lite-signal/issues/4)
        sub.dispatchEvent(getNewSignal(name, data));
      });
    }

    class LiteSignal extends Polymer.Element {
      static get is() {return "lite-signal"};

      connectedCallback() {
        super.connectedCallback();

        subscribers.push(this);
      }

      disconnectedCallback() {
        super.disconnectedCallback();

        var i = subscribers.indexOf(this);
        if (i >= 0) {
          subscribers.splice(i, 1);
        }
      }
    }
    window.customElements.define(LiteSignal.is, LiteSignal);

    // signal listener at document
    document.addEventListener('lite-signal', function(e) {
      notify(e.detail.name, e.detail.data);
    });

  })();
</script>