Is substring() method available in the String object in non global scope?

[SwarnadeepNandy]

I am using below code in some non global   application scope

current.floor   =   parseInt(current.room.substring(0,1)); // where 'room' is string type and 'floor' is integer type.

but it is not working, i am getting error

but when i am using

current.floor = parseInt(current.room.toString().substring(0,1));

it is working perfectly fine.

Why do i need to use toString() for a string type variable?

[SwarnadeepNandy]

Yes thats the thing. I thing for the security issues they have restricted access.