Some points

[zloirock]

• Set.isSharedArrayBuffer?O_o
• At this moment, we haven't (u)int64 in JS, by IEEE754 integers are safe in float representation only up to 2^53, for that we have Number.isSafeInteger, so adding Number.isInt64 and Number.isUint64 seems wrong.
• Where is String.isStringIterator?
• Generator object is not a function, so why isGeneratorObject should be in Function namespace?
• Adding isTypedArray and is(Int|Uint)(8|16|32|64)Array methods to [TypedArray] (%TypedArray%?) seems wrong - Uint8Array.isTypedArray(float32array) or Float32Array.isUint8Array(uint8array) confuses.
• Intl is not a part of ECMA262, so adding methods to it should be a proposal for ECMA402.

[jasnell]

• Point one fixed thanks to @addaleax :-)
• Noted. I'd already been considering pulling isInt64 and isUint64 back out.
• Can add isStringIterator tho I'm not sure we've seen any significant reason to call that one out in Node.js. Not sure there's much of a use case for it.
• Wasn't sure where else to put isGeneratorObject()... it could go on Object I suppose.
• Agree on the [TypedArray] methods. would like to have a better place to hang those off. Perhaps just make them specific... Uint8Array.isUint8Array(arg), Uint16Array.isUint16Array(arg) would be best...
• Agree on the Intl stuff... wanted to include those here for completeness but can engage with 402 directly on those.

[jasnell]

Updated to address this feedback

[zloirock]

👍

• String.isStringIterator required for consistancy with other methods.
• isTypedArray also should be moved... maybe to Object?

[jasnell]

Will add isStringIterator(). Will deal with the location of isTypedArray separately.