Add an API to focus on elements

[pranavkm]

A common ask from Blazor users is the ability to perform trivial DOM operations without having to manually write the JavaScript / JSInterop code. Having the ability to focus on DOM elements is one of the more popular ones that we'd like to address.

To solve this, we'd like to introduce FocusAsync() as an extension method to ElementRef types. Here's the usage we think would work the best:

@code {
  ElementRef myRef;

  protected override async Task OnAfterRenderAsync(bool first)
  {
      await myRef.FocusAsync();
      ...
   }
}

This would most likely use JSInterop for it's implementation, but it would be nice not to have to pass in the IJSRuntime instance.

Related issue with lots of feedback: #17472

[mrpmorris]

I wouldn't like to have to write code to focus an element. It would be better as a directive...

<input @autofocus/>

But I am not sure if it would be possible to make it work with custom components like <InputText>

[pranavkm]

@mrpmorris we have the linked issue open to consider addressing the autofocus attribute. We wanted to independently provide convenience APIs for focus and other DOM operations.