> It's definitely not under the hood. Really? I'd love to see some references to that. I know there's some operations to convert a javascript string to UTF8,

> It's definitely not under the hood. Really? I'd love to see some references to that. I know there's some operations to convert a javascript string to UTF8, but everything which measures a string counts using 2-byte UCS2 items. For example, array-style indexing, string.length, str.charCodeAt(), split(), slice(), indexOf(), etc. Also lots of DOM APIs use those weird string lengths too. For example, input element selectionStart / selectionEnd fields measure the selection range by counting surrogate pairs, not characters.