Return last word of string in JavaScript

This function returns last word of your string.
For example, your string = My lucky color will give you the result = color

function get_last_word(str, sep)
{
     var last_word = '';
     if (str != '')
     {
          sep = ( ! sep) ? '-' : sep;
          last_word = str.split(sep).splice(-1)[0];
     }
     return last_word;
}

Usage:

alert(get_last_word('My lucky color', ' '));

Note: 2nd parameter is an optional. By default it applies ‘-‘ (hyphen).