[6.x] Add disabled prop to Button component

[duncanmcclean]

This pull request adds a disabled prop to the Button component, like we have for Input.

Fixes #14022

[daun]

This might cause some accessibility issues in certain scenarios.

The ⁠disabled attribute removes the button from the tab order, meaning it can't be reached by keyboard navigation. This can be a problem if you're using a tooltip to explain why the button is disabled, since the user would need to tab to it to show the tooltip.

Using ⁠aria-disabled would keep the button in the tab order while still signalling a disabled state to screenreaders. The trade-off is that click events need to be blocked manually — both in CSS via ⁠pointer-events: none and in JS with ⁠event.preventDefault() — whereas ⁠disabled handles all of that automatically.

[duncanmcclean]

@daun Good catch, thanks! Just pushed up a version using aria-disabled instead.

[jasonvarga]

What's the point of a disabled attribute on a html element if you can't use it? I think if you want to tell a button to be disabled, it should disable it. If you want it to be just aria-disabled, then explicitly do that instead.

[daun]

@jasonvarga I guess disabled is a bit of a misnomer in that it hides the button instead of marking it as disabled for anyone using a screenreader or keyboard exclusively. That's fine where explicitly intended, but I'd argue it's better UX and A11y to keep the element tabbable/interactive and reading/showing some type of message that explains it's disabled and why.

As a user, I'd prefer tabbing to a button that reads "Submit, disabled" to not finding a submit button at all.

There's a few articles I found helpful when dealing with this in a recent project, e.g. Usability Pitfalls of Disabled Buttons and Making Disabled Buttons more Accessible.

[jasonvarga]

That's fine, but my point is that at the primitive component level, passing a disabled prop to it should just apply that.

If in the context of where you're using that button that you want to maintain tabindex/aria/etc, then using disabled is not appropriate, so don't use it.

[daun]

Right, good point, makes sense to keep things literal on the primitive layer.

It would be lovely if the above use-case was somehow supported by the UI layer though, e.g. using a focusable or focusableWhenDisabled prop as a shortcut for using aria-disabled instead of disabled. But I can always submit a PR if I care enough :)

<Button :disabled focusable v-tooltip="hint" @click="handleClick">Submit</Button>

vs

<span v-if="disabled" v-tooltip="hint" @click="handleClick" tabindex="0">
  <Button disabled>Submit</button>
</span>
<Button v-else @click="handleClick">Submit</button>