i have 3rd party lib returns baseclass.

i want add properties baseclass , use it. compile error.

var mysubclass : subclass = methodthatreturnsbaseclass();

compile error:type baseclass not assignable type subclass

interface subclass extends baseclass { title: string; }

how should written?

how should written?

one possibility:

interface subclass extends baseclass {     title?: string; }

another:

var mysubclass : subclass = <subclass>methodthatreturnsbaseclass();

i prefer method 1 more semantically correct