Key and Mouse Button events - modifiers that restrict the action of on:event

[lukaszpolowczyk]

Is your feature request related to a problem? Please describe.
Svelte greatly simplifies the code.
I miss the simplification of the recognition of a key or a mouse button - to make it even more transparent.
I'm trying on the line (maybe it's a bad idea, but I don't have a better one):

<button on:mouseup={event=>
	event.button===0?doSound(wave)
	:
	event.button===1?saveSound(wave)
	:
	null
}>

but this code is just... not very readable, and ugly.

Describe the solution you'd like

<!-- Mouse button modifiers (and @const in tag) -->
<button
	on:mouseup|firstButton={()=>doSound(wave)}
	on:mouseup|secondButton={()=>saveSound(wave)}
}>
	
<!-- Or maybe like a function? -->
<button
	on:mouseup|button(0)={()=>doSound(wave)}
	on:mouseup|button(1)={()=>saveSound(wave)}
}>

<!-- Key code modifiers -->
<svelte:window on:keydown|KeyA|KeyS|KeyD|KeyW={doSometing}/>
	
<!-- or from an array -->
{@const arr=["KeyA","KeyS","KeyD","KeyW"]}
<svelte:window on:keydown|{arr}={doSometing}/>
	
<!-- or like a function -->
<svelte:window on:keydown|keyCode(KeyA,KeyS,KeyD,KeyW)={doSometing}/>

<!-- or -->
{@const arr=["KeyA","KeyS","KeyD","KeyW"]}
<svelte:window on:keydown|keyCode(arr)={doSometing}/>

Describe alternatives you've considered

<script>
function mouseup (event) {
  event.button===0?doSound(wave)
  event.button===1?saveSound(wave)
  :
  null
}
</script>
<button on:mouseup>

How important is this feature to you?
I use this on a daily basis so quite important.

[Conduitry]

This came up before in #4427 and in other issues, and I still think that all the extra syntax (and extra documentation) that this would require is not worth it, compared to just doing this in javascript.

[lukaszpolowczyk]

@Conduitry How can you say unequivocally "worth it" or "not worth it"? Is it such an arbitrary decision?

I understand the concept of svelte simplicity and support it very much.
But there aren't many places like the concept of modifiers with parameters - it's something simple and general.
on:keydown|keyCode(KeyA,KeyS,KeyD,KeyW)

I will even say that there are a lot of things in svelte that can only be used occasionally, and sometimes you have to use a less neat version.
For example, you can
bind:value
but there are situations where you cannot do without
on:change={e=>value=e.target.value}
But we don't delete bind:value.

Such button and key modifiers would fit in perfectly.