Create onmounted Event

[ealmloff]

resolves #631
resolves #517
resolves #804
resolves #423

Implements a new onmounted event with a trait object in the HTML crate. (More API discussion in #631)

The element allows:

• The raw element type of the platform
• The position of the element
• Scrolling to the element
• Focusing the element
  Each of these APIs are optional for the underlying renderer to implement.

Todo:

• Create new event in html crate
• Platform specific implementations
  • Web
  • Desktop
  • Liveview
  • TUI
• Add example of onmounted event

[yusefnapora]

This looks so cool! I've been writing components that render svg shapes and have been using polling hacks to query JS for the the rendered size of the SVG element so I can calculate scaling factors, etc. Can't wait to toss that code out 😄 This seems like it will open up quite a few new possibilities.

[jkelleyrtp]

Awesome! Thank you! @Demonthos

[zoechi]

A bit late, but should the event name not be onmount?
All event names in the browser are in this form onmousemove onmouseenter, onkeypress, ...
I'm not aware of one event name in past tense.

I'm curious is there also an onunmount event (planned)?

[ealmloff]

A bit late, but should the event name not be onmount? All event names in the browser are in this form onmousemove onmouseenter, onkeypress, ... I'm not aware of one event name in past tense.

Yes, onmount would be more consistant. If you want to, you can open a PR to change it

I'm curious is there also an onunmount event (planned)?

Effects also run after the component is first mounted, but they don't provide information about the element that was mounted. That is what the onmount event adds.

Hooks are dropped when the component is dropped. You can use them to run any of your cleanup logic. We could defiantly provide a hook that makes it easier to run a closure when the component is unmounted. We could have a onunmount event that runs directly before the element is unmounted, but I can't think of a use case that would use the element.

[zoechi]

Hooks are dropped when the component is dropped.

Right, I remember seeing a comment in Discord where you mentioned that 🤦

I can't think of a use case that would use the element.

Right, the information I would be interested in is available in the components state anyway.