You can just use the string object like that.What are you trying to convert.
<cpde>
var stringObj = new String ("string");
you could just use this stringObj it would give you the value only.
More on JS Strings visit =>
http://www.w3schools.com/jsref/jsref_obj_string.asp[
^]
If you have number object you can use toString() method
something like -
var n= new Number(1);
n.toString();
Hope this helps.