16
What about just splitting the string at slashes and just replacing the values?
var myURL = '/blogs/1/2/all-blogs/', fragments, newURL;
fragments = myURL.split('/');
fragments[1] = 3;
fragments[2] = 8;
fragments[3] = 'some-specific-blog';
newURL = fragments.join('/');
That should return:
'/blogs/3/8/some-specific-blog'