The ES5 spec defines a string as being a series of UTF-16 code-units, which inherently means surrogates show through. APIs like that tend to be low priority be

The ES5 spec defines a string as being a series of UTF-16 code-units, which inherently means surrogates show through. APIs like that tend to be low priority because they aren't used by browsers (which pass everything through as UTF-16 code-units, typically treating them as possibly-valid UTF-16 strings).