wcwidth.js is a javascript porting of C's wcwidth()

 wcwidth.js is a simple javascript porting of wcwidth()
 implemented in C by Markus Kuhn.
 .
 wcwidth() and its string version, wcswidth() are defined by
 IEEE Std 1002.1-2001, a.k.a. POSIX.1-2001, and return the
 number of columns used to represent a wide character and
 string on fixed-width output devices like terminals.
 Markus's implementation assumes wide characters to be
 encoded in ISO 10646, which is almost true for JavaScript;
 almost because JavaScript uses UCS-2 and has problems
 with surrogate pairs. wcwidth.js converts surrogate pairs
 to Unicode code points to handle them correctly.
 .
 Node.js is an event-based server-side JavaScript engine.