Searching multiple words in a string

Hi,

I've got this code in my AS3 :

var str:String = mySharedObject.data.theDate;
var search:String = "monday";
var replace:String = ""; 
function strReplace(str:String, search:String, replace:String):String {
return str.split(search).join(replace);
}

Is it possible to tell the code to search for "monday or tuesday or wednsday, or thursday, or friday" and replace them with "_" ?

I would like to something like

var search:String ="tuesday","wednsday","thursday";

But it's not working..