Symbol history

[kai zhu]

> As far as the spec is concerned...
> 
> Symbols were introduced in draft 12 of ES6.
> They were defined as a kind of exotic object, stateless and immutable.
> 
> In draft 15, Symbol became a primitive type.
> In draft 16, it went back to being a kind of exotic object.
> In draft 19, it went back to being a primitive type.


can i ask why they were changed to primitive-type instead of exotic-object? what are the disadvantages of keeping symbols as objects (with an extra Object.isSymbol subtype-check)?

because one obvious advantage from what i see, is to avoid breaking backwards-compatibility with previously stable-code (since es1 in 1997 [1]) that rely on typeof checks:

```js
if (typeof foo === ...) {
    ...
} else {
    // break backwards-compatibility with stable-code since es1
    // due to unexpected symbol-case
    ...
}
```

[1] ECMA-262, 1st edition, June 1997
https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf <https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf>
kai zhu
kaizhu256 at gmail.com



> On 29 May 2018, at 3:33 PM, T.J. Crowder <tj.crowder at farsightsoftware.com> wrote:
> 
> Thanks all!
> 
> On Mon, May 28, 2018 at 7:36 PM, Michael Dyck <jmdyck at ibiblio.org <mailto:jmdyck at ibiblio.org>> wrote:
> > As far as the spec is concerned...
> 
> Thanks. Sorry Michael, I should have been more clear: I'm talking about the history _leading up_ to the spec.
> 
> On Mon, May 28, 2018 at 7:33 PM, Allen Wirfs-Brock <allen at wirfs-brock.com <mailto:allen at wirfs-brock.com>> wrote:
> > That's a pretty good summary
> 
> On Tue, May 29, 2018 at 2:51 AM, Allen Wirfs-Brock <allen at wirfs-brock.com <mailto:allen at wirfs-brock.com>> wrote:
> > A good starting point for researching the history is:
> > https://web.archive.org/web/20110505015255/http://wiki.ecmascript.org:80/doku.php?id=strawman:private_names <https://web.archive.org/web/20110505015255/http://wiki.ecmascript.org:80/doku.php?id=strawman:private_names>
> 
> Thanks Allen. If the summary was good enough, that's as much detail as I need to get into.
> 
> Thanks again all!
> 
> -- T.J. Crowder
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