Q: What is the difference between UCS-2 and UTF-16?
A: UCS-2 is obsolete terminology which refers to a Unicode implementation up to Unicode 1.1, before surrogate code points and UTF-16 were added to Version 2.0 of the standard. This term should now be avoided.
UCS-2 does not define a distinct data format, because UTF-16 and UCS-2 are identical for purposes of data exchange. Both are 16-bit, and have exactly the same code unit representation.
Sometimes in the past an implementation has been labeled “UCS-2” to indicate that it does not support supplementary characters and doesn’t interpret pairs of surrogate code points as characters. Such an implementation would not handle processing of character properties, code point boundaries, collation, etc. for supplementary characters.
EDIT: For anyone who may come across this, be sure to check out this link:
Specifications for ECMAScript versions 3 and 5 at least both explicitly declare a
String to be a collection of unsigned 16-bit integers and that if those integer values are meant to represent textual data, then they are UTF-16 code units. See
- section 8.4 of the ECMAScript Language Specification in version 5.1
- or section 6.1.4 in version 13.0.