Function constants for Identity and No-op

[Isiah Meadows]

I'll note that it's longer than just typing them out manually (and close if
they're aliased):

```js
Function.IDENTITY
IDENTITY
x => x

Function.NOOP
NOOP
() => {}
```

Not sure if it adds anything.

On Tue, Aug 9, 2016, 14:44 Eli Perelman <eli at eliperelman.com> wrote:

> I'm not sure if something like this has been proposed before, but I often
> find myself declaring constants for the identity function and the no-op
> function. I think it would be useful to have constants available on
> Function containing these values. For example `Function.IDENTITY` and
> `Function.NOOP`. Essentially these constants would map to:
>
> ```js
> Function.IDENTITY = (a) => a;
> Function.NOOP = () => null; // or:
> Function.NOOP = () => {};
> ```
>
> These could then be used in places where non-user-controlled APIs need
> default functions need to be executed, or as placeholders for default
> values that may be executed before a function has been supplied. For
> example:
>
> ```js
> // third-party API requires a callback or throws, but no functionality
> really needs to done:
> thirdParty.action(Function.NOOP);
>
> // Function needs a default which *may* execute prior to having a
> different one specified (contrived):
> const action = (handler = Function.IDENTITY, value = 10) => handler(value)
> ;
> ```
>
> Thoughts? Seems like something simple with positive value. Thanks!
>
> Eli Perelman
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