Proposal: `Object.isEmpty(value)`

Herby Vojčík herby at mailbox.sk
Thu Feb 14 10:43:12 UTC 2019


On 14. 2. 2019 7:54, Jordan Harband wrote:
> `Reflect.ownKeys(x || {}).length === 0`?

This seems to reify key list. That gist of the OP is probably to be able 
to be able to tell fast enough if it's empty.

Or are JS engines actually doing this fast (like returning "virtual" 
keys list for which they can tell .length fast and only actually reify 
the keys themselves lazily)?

Herby

> On Wed, Feb 13, 2019 at 10:31 PM Isiah Meadows <isiahmeadows at gmail.com 
> <mailto:isiahmeadows at gmail.com>> wrote:
> 
>     This would be roughly equivalent to `Object.keys(value).length === 0`,
>     but with a few exceptions:
> 
>     1. If `value` is either `null` or `undefined`, it gracefully falls
>     back to `false` instead of throwing an error.
>     2. It takes enumerable symbols into account, like `Object.assign`.
> 
>     So more accurately, it returns `false`  if the value is neither `null`
>     nor `undefined` and has an own, enumerable property, or `true`
>     otherwise.
> 
>     It's something I sometimes use when dealing with object-based hash
>     maps (like what you get from JSON, input attributes). I typically fall
>     back to the (partially incorrect) `for ... in` with a `hasOwnProperty`
>     check for string keys, but I'd like to see this as a built-in.
> 
>     There's also a performance benefit: engines could short-circuit this
>     for almost everything with almost no type checks. It's also an obvious
>     candidate to specialize for types.
> 
>     - If it's not a reference type (object or function), return `true`.
>     - If it's not a proxy object, or a proxy object that doesn't define
>     `getPropertyDescriptor` or `ownKeys`, it's often just a memory load,
>     even with dictionary objects and arrays.
>     - If it's a proxy object with `ownKeys` and/or
>     `getOwnPropertyDescriptor`, this is the slow path, but you can still
>     short-circuit when `ownKeys` returns an empty array.
> 
>     -----
> 
>     Isiah Meadows
>     contact at isiahmeadows.com <mailto:contact at isiahmeadows.com>
>     www.isiahmeadows.com <http://www.isiahmeadows.com>
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