If you only want to test for certain whitespace characters, do so manually, otherwise, use a regular expression, ie
/\s/.test(ch)
Keep in mind that different browsers match different characters, eg in Firefox, \s is equivalent to (source)
[ \f\n\r\t\v\u00A0\u2028\u2029]
whereas in Internet Explorer, it should be (source)
[ \f\n\r\t\v]
The MSDN page actually forgot the space 😉