求个正则表达式解决思路

var str = 'fds fs df <span style="color:#FF0000;"> fdsfsdfds</span>fdsf    sd <div a="s s"> f   dsd </div> ';
            var a = str.replace(/^[^<>]*<|>[^<>]*<|>[^<>]*$/g, function(){
                return arguments[0].replace(/\s/g, "&nbsp");
            });
            alert(a);