[amp-bind] amp-list evaluation does not wait for amp-state's src request to be resolved

[sebastianbenz]

Bindings are evaluated when an amp-list template is rendered. However, these bindings don't wait until an amp-state's remote src has been resolved (which they should to ensure an deterministic behavior).

Example:

An amp-state element using a JSON endpoint:

<amp-state id="favorite"
  credentials="include"
  src="/favorite-with-count?RANDOM">
</amp-state>

The amp-list binds an element to the amp-state:

<amp-list ... src="/favorite-with-count?RANDOM">
    <template type="amp-mustache">
        <div class="favorite-count" [text]="favoriteWithCount.count ? favoriteWithCount.count : ''">{{count}}</div>
    </template>
  </amp-list>

This results in a race-condition, where the text is either null or 123 depending on whether the amp-state has already been resolved or not.

I noticed this while working on this sample: https://ampbyexample.com/advanced/favorite_button/

//cc @choumx @ericlindley-g

[dreamofabear]

Good eye. 😄 This is an interesting one. The fundamental tension is the fact that both amp-state and amp-list elements are fetching the same data. Maybe we can add the ability for amp-list to explicitly reference an amp-state element by id as its data source.

[sebastianbenz]

If they’re fetching the exact same data it works due to request caching. Only when they’re different it may result in a race condition. Being able to reference state from amp-list without having to provide a src would be a lot cleaner. We’d still need to delay amp-list rendering until amp-state has been resolved though.

…

On Thu, 9 Nov 2017 at 20:04, William Chou ***@***.***> wrote: Good eye. 😄 This is an interesting one. The fundamental tension is the fact that both amp-state and amp-list elements are fetching the same data. Maybe we can add the ability for amp-list to explicitly reference an amp-state element by id as its data source. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#11998 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAXOOCova7ofyuRYe0FJk6OMlryH6bIEks5s01q4gaJpZM4QYMeE> .

[ampprojectbot]

This issue hasn't been updated in awhile. @choumx Do you have any updates?