introduce default type serializers

[43081j]

Fixes #264.

Maybe this is a solution?

• The old type option has been renamed to serializer
• type is now one of the primitive constructors (Boolean, String, Number, Object or Array) if set
• AttributeSerializer has been renamed to ComplexAttributeSerializer
• AttributeType has been renamed to AttributeSerializer
• AttributeType is a type alias for the basic primitive constructors
• Deserialization and serialization checks for a default serializer if none is specified and a type has been

This would reduce some confusion, especially for those coming from Polymer, as the type system will be almost the same (there is no support for Date). Additionally, much of the content out there about lit mistakenly uses type: Object often, so this alone tells me people are assuming that is the correct syntax already.

Examples:

@property({ type: Object })
@property({ serializer: (val) => customSerializer(val) })
@property({
  serializer: {
    toAttribute(val) { return `${val}`; },
    fromAttribute(val) { return JSON.parse(val); }
  }
});

When using something like type: Object, the following occurs:

el.myProp = { a: 5 }; // myprop='{"a":5}'
el.setAttribute('myprop', '{"a":6}'); // myProp === 6

If you have better ideas or other plans, im happy to close, just figured i'd push this since I had it.

cc @sorvell

[admwx7]

👍

[sorvell]

Thanks very much for the PR, it inspired the changes in #369. There were just a few more changes desired than seemed feasible to describe in a review so we incorporated your ideas into the other PR instead.

The serializers/deserializers there are almost exactly the same. One difference is that Polymer allows Object based properties to be non-objects which seems a little loser than we want here.

Other than that, instead of serializer (I realized I suggested that), we went with converter and decided to pass type to it. This way type is really just a hint for the converter.

We welcome your feedback on #369.