var bindif = [{

        "ifname": "Ge0/2/1",

        "ip": "20.1.1.1",

        "mask": "255.255.255.0"

    }, {

        "ifname": "Ge0/2/5",

        "ip6addr": "2000::254"

    }, {

        "ifname": "Ge0/2/5",

        "ip": "40.1.1.1",

        "mask": "255.255.255.0"

    }];

    var result = bindif.reduce(function (pre, curr) {

        var exist = pre.find(function (dt) {

            return dt.ifname === curr.ifname;

        });

        if(exist) {

            if(curr.ip && exist.ip6addr){

                    exist.ip = curr.ip;

                    exist.mask = curr.mask;

            }

            if(curr.ip6addr && exist.ip){

                exist.ip6addr = curr.ip6addr;

            }

        } else {

            pre.push(curr);

        }

        return pre;

    }, []);

    console.log(result);