IMO String.fromCodePoint should disallow U+D800-U+DFFF. There's already fromCharCode that does that, and a according to The Unicode Standard, isolated surrogates have no meaning on their own and goes on to compare them to illegal UTF-8 sequences. IMO "CodePoint" is a 21 Unicode code point, and explicitly not UTF-16, so it shouldn't confuse things by allowing UTF-16 (or other encoding) forms.
-Shawn -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Norbert Lindenberg Sent: Wednesday, December 12, 2012 1:25 PM To: Erik Arvidsson Cc: [email protected] Subject: Re: String.fromCodePoint and surrogate pairs? Do you know what the people who talked to you mean by "aware of UTF-16 code units"? As specified, String.fromCodePoint, accepts all UTF-16 code units because they use a subset of the integers allowed as code points (0 to 0xFFFF versus 0 to 0x10FFFF). For non-surrogate values, you get exactly what you expect. Surrogate values are interpreted as surrogate code points, which are valid code points in Unicode (their use makes a string ill-formed in Unicode terminology, but the proposed ECMAScript spec ignores issues of well-formedness for compatibility with ES5). Since in conversion to UTF-16 a surrogate code point just becomes the corresponding code unit, it can happen that two surrogate code points (an ill-formed sequence) become a well-formed surrogate pair: String.fromCodePoint(0xD83D, 0xDE04) => "\uD83D\uDE04" = "😄". The story for UTF-8 is very different: Of course all UTF-8 code units would be accepted by String.fromCodePoint, but they would turn into a completely different character sequence. E.g., the UTF-8 byte sequence for 😄: String.fromCodePoint(0xF0, 0x9F, 0x98, 0x84) => "\u00F0\u009F\u0098\u0084" = "ð\u009F\u0098\u0084" (the last three are control characters). Handling UTF-8 would require a way to identify the character encoding to convert from, which indicates the beginning of an encoding conversion API, and the internationalization ad-hoc decided not to work on one within ECMAScript. There is an API being defined as part of the encoding standard project at WhatWG. Norbert On Dec 12, 2012, at 7:46 , Erik Arvidsson wrote: > It was suggested to me that we could probably extend String.fromCodePoint to > be aware of UTF-16 code units too. It seems doable since the lead surrogate > is not a valid code point. > > The question is if it is worth it? It seems like we are going down a slippery > slope if we start to do things like this. Should we also handle UTF-8 code > units. Maybe it is better not to do this and try to get people to move away > from UTF-16 code units and move them towards code points. > > -- > erik _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
