[rgl]

var str='sdf23kdgbjk231890njsfjk0-sdfasdjkldfs';
alert(str.split(/\d/).length-1)

Вот что говориться про split в книге "javascript: The Good Parts"

There are some special cases to watch out for.
.....................
Some implementations suppress empty strings in the output array when the separator is a regular expression:

var f = '|a|b|c|'.split(/\|/);
// f is ['a', 'b', 'c'] on some systems, and
// f is ['', 'a', 'b', 'c', ''] on others