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Module Namespace Objects:

Various Oddities

Adam Klein

TC39

November 2016

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Overview

  • Module Namespace Objects are Exotic
    • Overrides nearly all operations
    • Mostly immutable (from the outside)
  • Also "exotic" in a couple other ways
    • null [[Prototype]] handling
    • Special @@iterator behavior

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@@iterator: issues

  • Utilizes CreateListIterator spec machinery, appears to be designed for spec-internal use
    • Each returned iterator object has its own "next" method, and no [[Prototype]]
    • next method does brand-checking on its receiver
  • The @@iterator function object itself is mutable
    • Matches up poorly with rest of Module Namespace Object design

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@@iterator: solutions

Either:

Remove @@iterator. Functionality is redundant with Object.keys()

Or:

Make @@iterator more like other iterators, and freeze the function

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@@toStringTag

Current state: [[Configurable]] is true, but [[Set]] and [[DefineOwnProperty]] fail

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Proposal: [[Configurable]] should be false

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[[SetPrototypeOf]]

Current state: Always returns false, even if argument is null

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Proposal: Match other spec behavior, returning true if argument is null