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 parameter. By default it assumes ‘-‘ (hyphen).