Better Support for AbortControllers

[loreanvictor]

Right now, the syntax for supporting abort controllers is a bit clunky:

let ctrl = new AbortController()

const data = observe(async $ => {
  const res = await fetch('https://my.api/?q=' + $(input), {
    signal: ctrl.signal
  })

  return await res.json()
}, () => {
  ctrl.abort()
  ctrl = new AbortController()
})

However, creating AbortControllers is not cheap, and so should only be done when the user demands it. Subsequently, the only way for handling this is to increase API surface and provide support for abortable observations:

const data = observeAbortable(async ($, singal) => {
  return await fetch('https://my.api/?q=' + $(input), { signal })
})

The observe() function can decide to include the signal or not based on the number of arguments provided in the expression, but this should be further investigated as it might be a bit clunky:

const data = observe(async ($, singal) => {
  return await fetch('https://my.api/?q=' + $(input), { signal })
})