fx-observer.html

<!--
    Copyright 2014 The Chromium Authors. All rights reserved.
    Use of this source code is governed by a BSD-style license that can be
    found in the LICENSE file.
 -->
<!--
    Sends and observes notifications by broadcasting notify events.

    Changing the `for` attribute dynamically is not supported and will cause
    leaks.

    Usage:

    <fx-observer for="example" on-notify="{{ handleHashChange }}"></fx-observer>

    FxObserver.notify("example", relatedData);

    FxObserver.notifyAsync("example", relatedData).then(function() {
        // ...
    });
-->
<link href="../polymer/polymer.html" rel="import">

<polymer-element name="fx-observer" constructor="FxObserver" attributes="for">
<script>
"use strict";
(function() {
    var instances = {};

    function registerInstance(object, type) {
        instances[type] = instances[type] || [];
        instances[type].add(object);
    }

    function unregisterInstance(object, type) {
        if (!instances[type])
            return;
        instances[type].remove(object);
    }

    function notify(type, data) {
        var receivers = instances[type] || [];
        for (var i = 0; i < receivers.length; ++i)
            notifyInternal(receivers[i], type, data);
    }

    // FIXME: Hack for v8 since it can't optimize functions with try/catch.
    function notifyInternal(receiver, type, data) {
        try {
            receiver.fire("notify", data);
        } catch (e) {
            console.log("Failed notification", type, e);
        }
    }

    function notifyAsync(type, data) {
        return Promise.resolve().then(function() {
            notify(type, data);
        });
    }

    Polymer({
        for: "",
        active: false,
        created: function() {
            this.style.display = "none";
        },
        attached: function() {
            registerInstance(this, this.for);
            this.active = true;
        },
        detached: function() {
            unregisterInstance(this, this.for);
            this.active = false;
        },
        notify: function(data) {
            if (!this.active)
                return;
            notify(this.for, data);
        },
        notifyAsync: function(data) {
            if (!this.active)
                return Promise.reject(new Error("Observer is detached"));
            return notifyAsync(this.for, data);
        },
    });

    document.addEventListener("polymer-ready", function() {
        // Static API
        FxObserver.notify = notify;
        FxObserver.notifyAsync = notifyAsync;
    });
})();
</script>
</polymer-element>