Two ways to count one string — code points vs UTF-16 code units

the string "🎵 between music and mathematics"

Python — counts code points

JavaScript — counts UTF-16 code units

Hover or tap a character to see its index in both systems.

The same word has two positions depending on who is counting. Python sees 🎵 as one character; JavaScript stores it as two UTF-16 code units, so every index after it disagrees by one — “music” starts at 10 on one side and 11 on the other.