var obj = {

        "objectiveDetailId": 285,

        "objectiveId": 29,

        "number": 1,

        "text": "x",

        "subTopics": [{

            "subTopicId": 1,

            "number": 1

        }, {

            "subTopicId": 2,

            "number": 32

        }, {

            "subTopicId": 3,

            "number": 22

        }]

    }

    var stToDelete = 2;

        _.remove(obj.subTopics, function(item, index, models) {

            return item.subTopicId === stToDelete;

        });

        _.remove(obj.subTopics, {

            subTopicId: stToDelete

        });