yarn-state-behavior.html

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

<script>
var YarnBehaviors = YarnBehaviors || {};

(function() {

  var internals = {
    instances: [],
    state: {}
  };

  /**
  This behavior should be used to share app state across elements via the `state` property.  The behavior ensures that path-notifying calls (e.g. `set()`, `splice()`, etc.) involving the `state` object or its children are delegated to all elements with this behavior, so observers should work as expected.

  @polymerBehavior YarnBehaviors.StateBehavior
  */
  YarnBehaviors.StateBehavior = {

    properties: {

      /**
       * An object shared among all elements with this behavior.
       */
      state: {
        type: Object,
        notify: true,
        readOnly: true,
        value: internals.state
      }

    },

    ready: function() {

      // Protect from state behavior being mixed-in with itself
      // see Polymer/polymer#1894

      if (this._usingStateBehavior) {
        return;
      }

      this._usingStateBehavior = true;


      // Patch _notifyPath to delegate to all instances.
      // This is slightly dirty, but by far most efficient
      // code-wise and perf-wise.

      if (typeof this._notifyPath !== 'function') {
        throw new Error('Polymer version appears to be incompatible with StateBehavior.');
      }

      var origNotifyPath = this._notifyPath;

      this._notifyPath = function() {

        // Call on self
        origNotifyPath.apply(this, arguments);

        // Call on all other instances if necessary
        if (arguments[0].split('.')[0] === 'state') {
          this._invokeInstances(origNotifyPath, arguments);
        }
      };

    },

    attached: function() {

      // Protect from state behavior being mixed-in with itself
      if (!~internals.instances.indexOf(this)) {
        internals.instances.push(this);
      }
    },

    detached: function() {

      var i = internals.instances.indexOf(this);

      if (i >= 0) {
        internals.instances.splice(i, 1);
      }
    },

    _invokeInstances: function(fn, args) {

      var instances = internals.instances;

      var instance;
      for (var i = 0; i < instances.length; i++) {
        instance = instances[i];
        if (instance !== this) {
          fn.apply(instance, args);
        }
      }
    }

  };

})();
</script>