This is necessary when a native property that sets an attribute should be observeable via attributeChangedCallback or Polymer property reflection (e.g. element.tabIndex = 5 setting the `tabindex` attribute).
Using this flag previously read attributes in the element constructor (in addition to patching setAttribute). This covers use cases except imperative or parser created custom elements (not upgraded). In that case the element will not have attributes in the constructor. This is addressed here by checking if the element has a parentNode (which will also not be true in these cases) and if so, records attributes at connected time. This is not always done to avoid having to filter out changes made by bindings.
* DisableUpgradeMixin: fIx finding superClass observedAttributes getter so that it's always correct
* Class: grab observedAttributes getter 1x off of LegacyElement
* Add tests for camelCase properties used with dash cased attributes.
Applies a number of optimizations that speed up defining a legacy element. These optimizations are mostly beneficial when a large number of elements are defined that are not used for initial render.
* Fixes an issue with `dedupingMixin` that was causing info to be cached on the resulting class even when no mixin should be applied.
* In Polymer.Class, avoids using `LegacyElementMixin(HTMLElement)` in favor of a cached `LegacyElement`.
* Copies `DisableUpgradeMixin` into Polymer's legacy class generation. This avoids the need to mix this on top of all legacy elements.
* Adds `legacyNoAttributes` setting which avoids setting `observedAttributes` and instead (1) applies the values of all attributes at create time, (2) patches set/removeAttribute so that they call attributeChangedCallback. This is faster since it avoids the work Polymer needs to do to calculate `observedAttributes`.
I am no longer an active maintainer of the Polymer repository, but I am still receiving review requests for PRs. While I could review PRs, it would be better for active maintainers to review community PRs. I am still available for reviews where my domain knowledge would be required, but I don't think I should be added a reviewer to every PR.
Steven Orvell
Kevin Schaaf
Daniel Freedman
Peter Burns
Tim van der Lippe