function common_extend(jsonbject1, jsonbject2) {
    let resultJsonObject = {};

    for (let attr in jsonbject1) {
        resultJsonObject[attr] = jsonbject1[attr];
    }

    for (let attr in jsonbject2) {
        // undefined is equivalent to no setting
        if (jsonbject2[attr] == undefined) {
            continue;
        }
        resultJsonObject[attr] = jsonbject2[attr];
    }

    return resultJsonObject;
}
extend two objects
@param {Object } jsonbject1
@param {Object } jsonbject2