In what JS engines, specifically, are toLowerCase & toUpperCase locale-sensitive?

Question

In the code of some libraries (e.g. AngularJS, the link leads to the specific lines in the code), I can see that custom case-conversion functions are used instead of the sta

Answer 1

Note: Please, note that I couldn't test it!

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As per ECMAScript specification:

String.prototype.toLowerCase ( )

[...]

For the purposes of this operation, the 16-bit code units of the Strings are treated as code points in the Unicode Basic Multilingual Plane. Surrogate code points are directly transferred from S to L without any mapping.

The result must be derived according to the case mappings in the Unicode character database (this explicitly includes not only the UnicodeData.txt file, but also the SpecialCasings.txt file that accompanies it in Unicode 2.1.8 and later).

[...]

String.prototype.toLocaleLowerCase ( )

This function works exactly the same as toLowerCase except that its result is intended to yield the correct result for the host environment’s current locale, rather than a locale-independent result. There will only be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode case mappings.

[...]

And as per Unicode Character Database Special Casing:

[...]

Format

The entries in this file are in the following machine-readable format:

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