Proposal: `Object.isEmpty(value)`

# Isiah Meadows (8 months ago)

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, www.isiahmeadows.com

# Jordan Harband (8 months ago)

Reflect.ownKeys(x || {}).length === 0?

# Herby Vojčík (8 months ago)

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)?

# Andrea Giammarchi (8 months ago)
  1. If value is either null or undefined, it gracefully falls back

to false instead of throwing an error.

I am having hard time logically thinking of an empty void as false:

Object.isEmpty(void 0) is false ?

I think keys(o || {}).length === 0 is a more explicit, ambiguity free, alternative.

isEmpty(null) === false when typeof null is still object also doesn't feel too right.

# Isiah Meadows (8 months ago)

I meant true for those - I had my conditions flipped. My bad.


Isiah Meadows contact at isiahmeadows.com, www.isiahmeadows.com

# Isiah Meadows (8 months ago)

They don't optimize this. Also, in an earlier reply, I mentioned I'm not a fan of that kind of hack, especially considering the obvious Reflect.ownKeys(x).length === 0 doesn't work when x is null/undefined, while for ... of does.

-----Isiah Meadowscontact at isiahmeadows.comwww.isiahmeadows.com