[Docs] Fix property type - function case

[vicb]

The serialization (.toAttribute) is handled by String at https://github.com/Polymer/lit-element/blob/4b20f80bc3145b0a0f7421f23d9a9f9e3d43e922/src/lib/updating-element.ts#L293-L298

[ghost]

@kenchris @justinfagnani Could you comment on this issue please?

My understanding from what @vicb points out is that this happens:

const MyObject = { 
  toAttribute: /* ... custom toAttribute */ 
  fromAttribute: /* ... custom fromAttribute */ 
};
const myFunction = /* ... myFunction */ ;
//...
// property declarations:
{ x: { type: Number } }  // serializer is String constructor, deserializer is Number constructor
{ y: { type: MyObject } } // serializer is custom toAttribute, deserializer is custom fromAttribute
{ z: { type: myFunction } } // serializer is String constructor, deserializer is myFunction

We also have:

// don't do this
{ w: { type: Object } } 
// Serializer is String constructor
// Deserializer is Object constructor, produces something weird e.g. { 0: "{", 1: "a", 2: ":", 3: "'", ... } 

Just wanted to check with you both because of this commit: b4c5f51

[ghost]

@sorvell fyi

[ghost]

Just saw this #369 which probably changes things

[vicb]

@katejeffreys yep it should change. I added a note there because it should have been updated.

Feel free to close this PR (maybe after #369 is updated ?)

[kevinpschaaf]

@vicb @katejeffreys I just added some more info regarding the change in #369 to #375 (comment)

[vicb]

lg