I'm curious if I've inferred the rationale for something correctly. The module namespace object properties for exports have `writable: true` in their property descriptors, but of course, they aren't writable (the module namespace object has its own [[Set]] implementation that returns false). I wondered why they weren't `writable: false`, so I went looking.
I found discussion in the March 24 2015 meeting notes about whether to even have `getOwnPropertyDescriptor` work. The consensus was yes, it should work (mixins!), and that it should report a basic data property that isn't configurable -- but is writable. Yahuda Katz points out that: > it is writable, but it's not writable by you though that's not always true (it may be declared `const`; that information isn't leaked from the module, though). In the May 25 2017 notes I found a comment from Mark S. Miller in relation to `writable: true`: > Non-writeable provides guarantee. Writable provides no guarantee. And this exchange between Yahuda Katz, Allen Wirfs-Brock, and Adam Klein: > YK: There is a a new property that we define as writable that is not writable. > > AWB: Not new. > > AK: Since... Proxys! There was some discussion of considering some flag basically saying what YK said, e.g., it's writable, but not by you :-) -- but that was more a brief digression that didn't go anywhere. So, then, what I infer is: They're marked writable because: 1. They may be writable by the exporting module, so code can't assume the value won't change; `writable: false` would make that assumption valid 2. Whether or not they're writable by the exporting module isn't information that should leak out of it 3. Non-writable `writable: true` data properties were already a thing (Proxies) So the most sensible thing was `writable: true` rather than `writable: false`. How'd I do? :-) -- T.J. Crowder
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