FW: JSON.stringify replacer array semantics

Douglas Crockford douglas at crockford.com
Mon Jun 8 18:06:02 PDT 2009

Allen Wirfs-Brock wrote:
> Doug and Rob, 
> Did you have any opinion on these two item (see below):
> 1) should the content of an replacer array be copied at the start of stringify such that it can't be side-effected during stringify processing? Oliver claims that FF 3.5 does such an internal copy and that json2.js also does so.  IE8 does not make a copy and my reading of json2.js (pulled today from json.org) disagrees with Oliver's (I think it doesn't copy). 
 > However, making a copy does seem like a reasonable thing to specify.

If I could have written json2.js using the ES5 language, I would have used 
Object.keys, not for..in, to obtain the keys. I think it would be good to avoid 
the side effect hazard that for..in is subject to, particularly in the presence 
of mutating getters.

> 2) should ToString be applied to the elements of an replacer array?
 > Currently this is not done in the ES5 spec.  Oliver reports that FF 3.5 does 
 > IE8 does not.  json2.js does not.  Is this a reasonable departure from the 
json2.js implementation?

It seems like an unnecessary step to me. Perhaps it would be better to throw?

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