Static properties in Polymer - polymer

Question

I'm trying to create a service in Polymer but I don't understand how I'm supposed to create static properties.
I would need them to share the same value for all instances ("static") BUT I would also need the observers to be triggered on every instance when they are updated.
I know I could create a variable in the scope of the Polymer() call like this :
var users = [];
Polymer({
is: 'my-service',
properties: {
users: {
type: Array,
value: users,
notify: true,
}
},
// ...
});
But it doesn't meet the second criteria. If I update it from one instance, it doesn't trigger the observers of the other instances.
Do you know how to perform that without triggering the observers on each instance manually ? (I could do it but it would defeat the idea of using a framework in this case.)
EDIT: An alternative would be to create a singleton, but I don't think it's possible.

Answer 1

It is actually quite simple to create static properties with observers. The issue that you are running into is a combination of the design of Polymer and the native implementation of Array.prototype methods.
Arrays and Object observers (deep/path observers) work a little differently than other property observers. In general, notify will only work when the instance changes. Additionally, most Array.prototype.functions return a new instance of the modified array... So, when you splice the array, a different instance is set into the object's property value (not the static property's value) and is now no longer equal to the original static array that you set. This is why only the modifying instance is notified.
My only recommendation to overcome this is: Don't use Array.prototype.splice(), or this.splice(). Even if you do this upon the static property, the result will always be a new array causing incongruous data. From here, you have two options: use Polymer's set API or delete the index and manually notifyPath()
Here is the link that discusses both:
Data binding - Path change notification

Answer 2

<dom-module id="my-service">
<template>
<iron-meta id="my-service-users" value="{{users}}"></iron-meta>
</template>
<script>
Polymer({
is: 'my-service',
properties: {
users: {
type: Array,
value: function(){return [];},
notify: true
}
}
});
</script>
</dom-module>
iron-meta creates a singleton value that automatically updates the users value in all instances, which should also trigger any relevant observers.