Function constants for Identity and No-op

[Eli Perelman]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20160809/3456354b/attachment.html>