Can I depend on the behavior of charCodeAt() and fromCharCode() to remain the same?

Question

I have written a personal web app that uses charCodeAt() to convert text that is input by the user into the relevant character codes (for example ⊇ is converted to 8839 for storage), which is then sent to Perl, which sends them to MySQL. To retrieve the input text, the app uses fromCharCode() to convert the numbers back to text.

I chose to do this because Perl's unicode support is very hard to deal with correctly. So Perl and MySQL only see numbers, which makes life a lot simpler.

My question is can I depend on fromCharCode() to always convert a number like 8834 to the relevant character? I don't know what standard it uses, but let's say it uses UTF-8, if it is changed to use UTF-16 in the future, this will obviously break my program if there is no backward compatibility.

I know that my ideas about these concepts aren't that clear, therefore please care to clarify if I've shown a misunderstanding.

Answer 1

fromCharCode and toCharCode deal with Unicode code points, i.e. numbers between 0 and 65535(0xffff), assuming all characters are in the Basic-Multilingual Plane(BMP). Unicode and the code points are permanent, so you can trust them to remain the same forever.

Encodings such as UTF-8 and UTF-16 take a stream of code points (numbers) and output a byte stream. JavaScript is somewhat strange in that characters outside the BMP have to be constructed by two calls to toCharCode, according to UTF-16 rules. However, virtually every character you'll ever encounter (including Chinese, Japanese etc.) is in the BMP, so your program will work even if you don't handle these cases.

One thing you can do is convert the numbers back into bytes (in big-endian int16 format), and interpret the resulting text as UTF-16. The behavior of fromCharCode and toCharCode is fixed in current JavaScript implementations and will not ever change.

Answer 2

I chose to do this because Perl's unicode support is very hard to deal with correctly.

This is ɴᴏᴛ true!

Perl has the strongest Unicode support of any major programming language. It is much easier to work with Unicode if you use Perl than if you use any of C, C⁺⁺, Java, C^♯, Python, Ruby, PHP, or Javascript. This is not hyperbole and boosterism from uneducated, blind allegiance.; it is a considered appraisal based on more than ten years of professional experience and study.

The problems encountered by naïve users are virtually always because they have deceived themselves about what Unicode is. The number-one worst brain-bug is thinking that Unicode is like ASCII but bigger. This is absolutely and completely wrong. As I wrote elsewhere:

It’s fundamentally and critically not true that Uɴɪᴄᴏᴅᴇ is just some enlarged character set relative to ᴀsᴄɪɪ. At most, that’s true of nothing more than the stultified ɪsᴏ‑10646. Uɴɪᴄᴏᴅᴇ includes much much more that just the assignment of numbers to glyphs: rules for collation and comparisons, three forms of casing, non-letter casing, multi-codepoint casefolding, both canonical and compatible composed and decomposed normalization forms, serialization forms, grapheme clusters, word- and line-breaking, scripts, numeric equivs, widths, bidirectionality, mirroring, print widths, logical ordering exclusions, glyph variants, contextual behavior, locales, regexes, multiple forms of combining classes, multiple types of decompositions, hundreds and hundreds of critically useful properties, and much much much more‼

Yes, that’s a lot, but it has nothing to do with Perl. It has to do with Unicode. That Perl allows you to access these things when you work with Unicode is not a bug but a feature. That those other languages do not allow you full access to Unicode can by no means be construed as a point in their favor: rather, those are all major bugs of the highest possible severity, because if you cannot work with Unicode in the 21st century, then that language is a primitive, broken, and fundamentally useless for the demanding requirements of modern text processing.

Perl is not. And it is a gazillion times easier to do those things right in Perl than in those other languages; in most of them, you cannot even begin to work around their design flaws. You’re just plain screwed. If a language doesn’t provide full Unicode support, it is not fit for this century; discard it.

Perl makes Unicode infinitely easier than languages that don’t let you use Unicode properly can ever do.

In this answer, you will find at the front, Seven Simple Steps for dealing with Unicode in Perl, and at the bottom of that same answer, you will find some boilerplate code that will help. Understand it, then use it. Do not accept brokenness. You have to learn Unicode before you can use Unicode.

And that is why there is no simple answer. Perl makes it easy to work with Unicode, provided that you understand what Unicode really is. And if you’re dealing with external sources, you are doing to have to arrange for that source to use some sort of encoding.

Also read up on all the stuff I said about 𝔸𝕤𝕤𝕦𝕞𝕖 𝔹𝕣𝕠𝕜𝕖𝕟𝕟𝕖𝕤𝕤. Those are things that you truly need to understand. Another brokenness issue that falls out of Rule ^#49 is that Javascript is broken because it doesn’t treat all valid Unicode code points in exactly the same way irrespective of their plane. Javascript is broken in almost all the other ways, too. It is unsuitable for Unicode work. Just Rule ^#34 will kill you, since you can’t get Javascript to follow the required standard about what things like \w are defined to do in Unicode regexes.

It’s amazing how many languages are utterly useless for Unicode. But Perl is most definitely not one of those!