Javascript inheritance for given syntax

I often see the following syntax in libraries, but then no inheritance. Now how can I define an ObjB that is inherited from ObjA and adds its own variables and methods?

(function() {

    'use strict';

    var ObjA = function(o) {
        var self = this;

        self.init(o);
    };

    ObjA.prototype = {
        init: function(o) {
            var self = this;

            self._x = o.x || false;
            self._y = o.y || false;

            return self;
        }
        // More methods...
    }

    if (typeof global !== 'undefined') {
        global.ObjA = ObjA;
    } 
    else if (typeof window !== 'undefined') {  
        window.ObjA = ObjA;
    }

})();