They're UTF-16, and substr(), length, etc, work at the code unit level. Hence, the above isn't actually valid for all strings - any characters that are represen

They're UTF-16, and substr(), length, etc, work at the code unit level. Hence, the above isn't actually valid for all strings - any characters that are represented by codepoints between U+10000 and U+10FFFF require 2 code units [1]. For example U+10429 Deseret Small Letter Long E [2] > '𐐩'.substr(0, 1) '\ud801' > '𐐩'.length 2 [1] https://en.wikipedia.org/wiki/UTF-16#Description https://en.wikipedia.org/wiki/UTF-16#Description [2] https://codepoints.net/U+10429 https://codepoints.net/U+10429