In summary, Unicode code points (characters) are 32 bit. JavaScript manipulates Unicode in utf-16 for historical reasons, because at some point before Unicode, 16 bit was deemed enough (ucs-2). utf-16 run length encodes Unicode 32 codepoints into one or two code units. Splitting in a middle of a codepoints produces one invalid half string, and one semantically different half string.

emojies are a sequence of Unicode codepoints producing a single grapheme. Splitting in the middle of a grapheme will produce two valid strings, but with some funky half baked emoji. So for a text editor it makes sense to split between grapheme boundaries.

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chrismorgan an hour ago | parent [-]

> Unicode code points are 32 bit

21-bit, actually. It was supposed to be 32-bit, but UTF-16 caps out at 21-bit, so they lopped eleven bits of potential from Unicode (and UTF-8, so no more six-byte encoding).

> at some point before Unicode

No, in the early days of Unicode.

> run length encodes

Um… what? RLE is a data compression thing, UTF-16 has nothing to do with it.

	▲	Someone 15 minutes ago \| parent [-]
		>> Unicode code points are 32 bit > 21-bit, actually Less than that. https://en.wikipedia.org/wiki/Code_point#In_character_encodi...: “The Unicode code space is divided into seventeen planes (the basic multilingual plane, and 16 supplementary planes), each with 65,536 (= 2¹⁶) code points. Thus the total size of the Unicode code space is 17 × 65,536 = 1,114,112” That makes it log(1,114,112)/log(2) bit. That’s about 20,09. (https://www.unicode.org/versions/Unicode17.0.0/ assigns 159,801 of them to characters)