Method observer on array property of element using MutableData is called twice on set.

[slindeneau]

Description

Using a method observer that observers all related changes to path (ex: prop.* ) will cause the method observer to fire twice for the base property value on set.

ex:

    static get properties() {
        return {
            arrayData:{
              type:Array,
              notify:true
            }
        };
    }
    static get observers() {
      return [
        '_arrayObserver(arrayData.*)'
      ]
    }

The observer will be called twice

Live Demo

Polymer 3 live demos exist?

Used polymer demo as base, check out the demo/child-element and demo/demo-element
https://github.com/slindeneau/poly-observer-bug

Steps to Reproduce

0. child-element has method observer on wildcard array mutation
1. child-element uses the mixin MutableData
2. child-element has a property that has notify: true
3. parent-element uses two-way data binding to bind that property to one of its properties.
4. child-element sets property value
5. child-element method observer is called twice

Expected Results

Method observer is called once for the base element

Actual Results

Method observer is called twice for the base element

Browsers Affected

• [ x] Chrome
• Firefox
• Edge
• Safari 11
• Safari 10
• IE 11

Versions

@polymer/polymer@3.0.5
@webcomponents/webcomponentsjs@1.2.6

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed after being marked stale. If you're still facing this problem with the above solution, please comment and we'll reopen!