What is the alternative for createProperty?

[MarkoZabcic]

Just upgraded to version 3.x and we get following warning in console:

reactive-element.js:46 Overriding ReactiveElement.createProperty() is deprecated.
The override will not be called with standard decorators
See https://lit.dev/msg/no-override-create-property for more information.

We have ApplicationElement as a base class for all other elements and we've implemented CustomConverter via createProperty API.

export class ApplicationElement extends LitElement {
  static createProperty(name, options) {
    super.createProperty(name, { converter: CustomConverter, ...options });
  }
}

How should we solve this without createProperty?

[augustjk]

That's an excellent question. Pinging @justinfagnani and @rictic to see if they might have thoughts.

Currently using the static properties block or experimental TypeScript decorators will still call createProperty. This deprecation is in preparation for removing the static properties block and moving completely over to standard decorators when the feature has been available in all major browsers which will be way way in the future (likely years).

I think the alternative to overriding createProperty for use with standard decorators would have to be creating your own version of the @property() decorator. It could wrap the existing one here

lit/packages/reactive-element/src/decorators/property.ts

Line 198 in a19a60b

export function property(options?: PropertyDeclaration): PropertyDecorator {

but provide an alternate default options.

This does change the ergonomics such that users now have to use a different decorator rather than extend from the base class with the overridden createProperty. Unfortunately I can't think of an override that will now target both static properties and decorators at the same time.

p.s. Apologies for the missing doc on this. We do have an outstanding issue to address missing warning messages.

[MarkoZabcic]

Thank you for quick response. That's good enough solution for future as we won't mix usage of decorators and static properties

It's worth mentioning that our main goal was to inject CustomConverter for attributes for all elements. Other than that we don't really need direct usage of createProperty. So if there would be better way to create centralized custom converters for attributes that we don't have to specify per property that would be also good.