无法使用Firebase交易功能更新对象

Question

我想使用Firebase事务功能更新对象。我阅读了所有文档和所有可用资源。如果特定节点上有数据，则事务功能下方的功能是从该节点删除数据。有人可以帮我吗，下面的代码有什么问题？

注意：-使用事务而不是更新功能，因为可以同时更新值。

    await refRun.once('value', snap => {
                    console.log(snap.val()); // Here I am able to get data
                })

   refRun.transaction(async (current) => {

    if (current === null) {
        console.log("coming", current);

        // updating values by fetcing from node 
        return await refRun.once('value', function (snapshot) {
            console.log("coming", snapshot.val()); // coming null here 
            if (snapshot.val() === null) {

                console.log("coming----1", snapshot.val());
                return {
                    total_raised: workout.run_amount || 0,
                    total_distance: workout.distance || 0.0
                }
            }
            else {
                console.log("coming----2", snapshot.val());
                return {
                    user_total_raised: snapshot.val().user_total_raised + workout.run_amount || 0,
                    user_total_distance: snapshot.val().user_total_distance + workout.distance || 0.0
                }
            }
        })

    }
console.log("coming-123", current); // null 

});