how to use json array key to javascript variable

how to use json array key to javascript variable

i am try json_encode($updateArray);
and this is call by ajax and after ajax success
return me json string on responseText something like this type

{"title":"superAdmin","id":"50"}
now i want to use this two key
like

var text = title;
var id = id;
who can i user this two to as diff. variable.
thanks.