Allow unused vars in object destructuring with rest property

[khankuan]

Hi, I've a question for the following syntax:

const { a, b, ...others } = obj;

This is useful to filter out certain keys in an obj. However, it does create 2 unused variables. Wanted to know the alternative that others might use.

Cheers :)

[LinusU]

Which is the two you don't want? You can just do like this and it will only extract those variables.

const { a, b } = obj

[khankuan]

I need others but not a and b.

[jprichardson]

@LinusU I think @khankuan is asking about about blacklisting certain object keys and keeping the rest. In many cases, you may not know exactly which key/vals you want, as the object may contain many different pairs, but you definitely know what you don't want.

Hopefully this lame contrived example demonstrates:

function getUserDataToDisplay () {
  const { secretKey, ...userData } = fetchFromDatabase()
  return userData
}

My solution would be that this is attempting to be too clever and the intent is not made clear. Rather, something like this would be better:

function getUserDataToDisplay () {
  // magic function blackList is defined somewhere...
  return blackList(fetchFromDatabase(), 'secretKey')
}

as this clearly communicates the intent to future readers (even yourself) of the code.

[dcousens]

@jprichardson

// magic function blackList is defined somewhere...

https://github.com/dcousens/blacklist, may or may not fit the syntax you want

[rszewczyk]

Also:

https://lodash.com/docs#omit
http://ramdajs.com/0.21.0/docs/#omit

[rstacruz]

How about:

const { secret: _, ...data } = foo

That's how it'd be done on elixir, don't know if standard allows it though!

On Thu, Jun 30, 2016, 11:59 PM Rob Szewczyk notifications@github.com
wrote:

Also:

https://lodash.com/docs#omit
http://ramdajs.com/0.21.0/docs/#omit

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[rszewczyk]

@rstacruz

I tried that at first (almost posted that exact example), but that actually binds the value of secret to a variable named _

[simonkberg]

Relevant discussion with usage examples: Hacker0x01/react-datepicker#517 (comment)
An option that allow this pattern has been discussed but postponed by ESLint until the es proposal has progressed further: eslint/eslint#4880 (comment)

[feross]

What if we update varsIgnorePattern so that _ is ignored? Then this would work:

const { secret: _, ...data } = foo

[feross]

Scratch that -- that wouldn't work for ignoring two keys:

const { secret: _, secret2: _, ...data } = foo

Let's just wait for ESLint to add first-class support for this. This is an experimental language feature anyway.

Blocked on: eslint/eslint#4880

[qzb]

@feross Why experimental? It's part of current standard and it's supported by current versions of node.js, chrome, firefox and even egde 😛

[simonkberg]

@QZD we're talking about the "Rest/Spread Properties" proposal which is currently in stage 2 https://github.com/tc39/proposals

[qzb]

@simonkberg @feross Sorry, my bad.

[feross]

Trying to clean up the open issues on this repo. This issue should be reevaluated when Rest/Spread Properties becomes part of the official language standard and ESLint adds a rule to support this usage. I would keep an eye on eslint/eslint#4880 to see if there's a new issue/PR posted that implements this functionality.