lit/lit-element v2.3.0 on GitHub

Added a static getPropertyDescriptor method to allow easier customization of property accessors. This method should return a a PropertyDescriptor to install on the property. If no descriptor is returned, no property accessor is created. (#911)
The value returned by render is always rendered, even if it isn't a TemplateResult. (#712)

Added @queryAsync(selector) decorator which returns a Promise that resolves to the result of querying for the given selector after the element's updateComplete Promise resolves (#903).
Added enableUpdating() to UpdatingElement to enable customizing when updating is enabled #860.
Added @queryAssignedNodes(slotName, flatten) decorator to enable querying assignedNodes for a given slot #860.
Added getStyles() to LitElement to allow hooks into style gathering for component sets #866.

Ensure UpdatingElement allows updates when properties are set after calling super.update().
LitElement renders when updates are triggered as a result of rendering (#549).
Properties annotated with the eventOptions decorator will now survive property renaming optimizations when used with tsickle and Closure JS Compiler.
Moved style gathering from finalize to initialize to be more lazy, and create stylesheets on the first instance initializing #866.
Fixed behavior change for components that do not implement render() introduced in (#712) (#917)