[Proposal] Optional chaining

Beknar Askarov beknaraskarov at gmail.com
Fri Aug 23 01:01:13 UTC 2019


Problem

Spreading is great! It contributes towards "declerativity" of the language
and reduces verbosity. I see one more feature to add to improve it.

Consider following

[
  1,
  condition && 2,
  condition && 3,
  4,
].filter(Boolean) // filtering needed to remove falsy values
// Results in
[1, 2, 3, 4] // if condition is `truthy`// and
[1, 4] // if not truthy.

Another way to achieve the same result without the need of filtering after

[
  1,
   ...(condition ? [2, 3] : []), // note extra [] in the end, to avoid errors
  4,
]

Similar pattern with objects

{
  ...(condition ? { foo: 'bar' } : {}), // extra {}
}

Another pattern is when condition is the object itself, when it is known
that type is one or falsy

[
  item1,
  item2,
  ...(itemsOrNull || []) // extra []
]

Similar for objects

{
  ...(obj || {}), // extra {}
}

I see these patterns appearing very often. And these are cleanest examples
I have seen so far.
ProposalOptional spreadingWith condition

// Arrays
[
  1,
  ?...(condition && [2, 3]), // no extras:)
  3,
]// Objects
{
  ?...(condition && { foo: 'bar' }) // no extras:)
}

When condition is the object

[
  item1,
  item2,
  ?...itemsOrNull // no extras at all:) even (...)
]

These look nicer and can be good for performance since (?...), since no
cleanup is needed after to remove falsy values or extra spreading even when
it is not needed.

Looks intuitive (since: https://github.com/tc39/proposal-optional-chaining)
Plays nice with typeings.

What do you think? https://es.discourse.group/t/optional-spreading/93
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