JavaScript regex for stripping leading & trailing whitespaces

I’m sure there are a bunch of libraries that do this, but sometimes wrestling with regexes is fun.

> var str = "           This string has some mighty fine whitespace.       ";
> str
'           This string has some mighty fine whitespace.       '
> str.replace(/^(\s*)((\S+\s*?)*)(\s*)$/,"$2");
'This string has some mighty fine whitespace.'