JS and Python are still old enough to have been created when Unicode was in its infancy, so they have their own share of problems from using UCS-2 (such as inde

JS and Python are still old enough to have been created when Unicode was in its infancy, so they have their own share of problems from using UCS-2 (such as indexing strings by what is now a UTF-16 code unit, rather than by a codepoint or a grapheme cluster). Swift has been developed in the modern times, and it's able to tackle Unicode properly, e.g. makes distinction between codepoints and grapheme clusters, and steers users away from random-access indexing and having a single (incorrect) notion of a string length.