fix(parent/child): Add host argument to parent and child factories.

[au-z]

Hi @smalluban!

Here's a totally unsolicited (but helpful) feature which you might find complementary to the existing parent/children factories...

For some complex components which reference parent and child elements based on element context, access to the host element is helpful. This can be done without a breaking change and creates some options for advanced component interactions.

For example, to get a parent which exposes a particular property name:

const MyChildComponent = define({
  tag: 'my-child-component',
  context: '__ctx__',
  contextProvider: parent((el, {context}) => el.hasOwnProperty(context)),
  // ...
})

Another use case:

const ChildElementCounter = define({
  tag: 'child-element-counter',
  childTag: '',
  children: children((el, {childTag}) => el.tag.toLowerCase() === childTag),
  // ...
})

Have a look and let me know what you think. Thanks! 👍

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit cd2259d:

Sandbox	Source
Hybrids web components playground	Configuration

[coveralls]

Coverage remained the same at 100.0% when pulling cd2259d on auzmartist:parent-child-context into 92fc366 on hybridsjs:master.

[smalluban]

Hi @auzmartist!

Thanks for your time in creating this PR. At first, i thought that it might be a not really useful feature, or it even might not work as you expect it, but after looking at this for a while, I can't make a reasonable argument against it.

I will merge the feature, but we need some changes:

• Create tests where the value from host changes, so the children/parent is updated (as null, or an empty array)
• there is API reference in docs, please update it as well (https://github.com/hybridsjs/hybrids/blob/master/docs/misc/api-reference.md)

[au-z]

Alright, I've added a couple more tests and added to the API docs. Ready for re-review @smalluban. 👍

[smalluban]

Nice work, thanks!