dom-repeat is wrong when attached/detached

[kolesoffac]

Description

When i use <dom-repeat>, and when i remove item from items, in detached-method use last id.

Live Demo

https://codepen.io/anon/pen/ZJEXqB

Steps to Reproduce

Example:

1. Load the page in the demo above.
2. Observe "attached the DOM! - " logged in the console
3. Press the button marked Remove first item

Expected Results

"attached the DOM! - " "0"
"attached the DOM! - " "1"
"attached the DOM! - " "2"
"detached the DOM! - " "0"

Actual Results

"attached the DOM! - " "0"
"attached the DOM! - " "1"
"attached the DOM! - " "2"
"detached the DOM! - " "2"

Browsers Affected

• Chrome
• Firefox
• Edge
• Safari 9
• Safari 8
• IE 11

Versions

• Polymer: v2.0.2
• webcomponents: v1.0.0

[sorvell]

I believe this is the same basic issue as #1713. There's a fix in the works. @kevinpschaaf can you verify?

[TimvdLippe]

We have analyzed your use-case and understood the "unexpected behavior". <dom-repeat> reuses element nodes for performance reasons. The assumption that the property layer remains the same throughout the lifecycle of the custom elements thus becomes incorrect. As such, whenever layer changes, in the oberserver you need to update the value of id as well.

You can in the future workaround this issue with using the feature restamp on <dom-repeat>, which is tracked on #1713. Therefore I am closing this issue, feel free to subscribe to #1713.