var str = "I'm a very^ we!rd* Str!ng.";
$('body').html(str.replace(/[^a-z0-9\s]/gi, " ").replace(/^\s+|\s+$|\s+(?=\s)/g, "").replace(/[_\s]/g, "-").toLowerCase());
First regex remove special characters with spaces than remove extra spaces from string and the last regex replace space with "-"