Data should be reset when the pattern no longer matches.

[jishi9]

The current behavior is problematic, particularly when combined with <iron-pages>

For example:

<app-route
    route="{{route}}"
    pattern="/:page"
    data="{{routeData}}"
</app-route>

<iron-pages selected="{{routeData.page}}"
            attr-for-selected="page"
            fallback-selection="default">
  <div page="a">PageA</div>
  <div page="b">PageB</div>
  <div page="default">Default page</div>
</iron-pages>

The current behavior:
When visiting http://foo/ we land at the default page.
Switching the URL to http://foo/b we land at Page B
Switching the URL back to http://foo/ (e.g. by clicking the browser's back button) , we still remain on Page B, when the expected behavior is to go back to the default page.

[cdata]

Agreed, the current behavior is problematic. Unfortunately, the current behavior is also working as designed. The stated intention of the designer was to avoid causing deep trees of state to thrash as routes become activated and deactivated. It is a nice idea, but in practice should probably be a secondary quality to "state changes the way I expect..." but I digress.

Given that this element already has had its major release, could you please propose this change in a way that retains backwards compatibility with default behavior? In other words, we can consider this change more seriously if it is "enabled" by an optional boolean attribute on the route.

[cdata]

/cc @e111077 who is the owner of this element

[e111077]

@cdata has a good grasp of this. This causes a lot thrashing down the tree, and then causes a lot of reported issues that they cannot keep state on their app / flashing of content after page change.

Though, this is also a common feature request that we've seen.

I'll be more-inclined to hide this behind a flag e.g. clear-data-on-inactive. That defaults to false / is opt-in.

Also want to cc @rictic initial designer of this element as he was the one to initially make this decision.

[cdata]

I'm with @e111077 on this - let's implement this change behind a flag. Please update the PR add an attribute flag to toggle this behavior!