无法在变量中存储JSON

我无法在变量中存储JSON。当我调用getIndividualMatchJSONObjHelper函数时，json变量本身会打印出来，但变量外部不会存储任何内容。如何在matchParticipantData.specificParticipantData中正确存储JSON变量

function getIndividualMatchJSONObj(matchData) {
   var matchParticipantData = {
        specificParticipantData: [numberOfGames]
    };

    for (var i = 0; i < numberOfGames; i++) {
       getIndividualMatchJSONObjHelper(matchData, matchParticipantData, i, function(err, json) {
            matchParticipantData.specificParticipantData[i] = json;
   });
} 
    return matchParticipantData;

}

function getIndividualMatchJSONObjHelper(matchData, matchParticipantData, indexIter, callback) {
    var individualMatchURL = 'https://na1.api.riotgames.com/lol/match/v3/matches/' + matchData.matchID[indexIter] + '?api_key=' + API_KEY;
    var jsonFinal;
     async.waterfall([
        function (callback) {
            request(individualMatchURL, function (err, response, body) {
                if (err)
                    return callback(err);
                if (response.statusCode != 200)
                    return callback(new Error('Status code was ' + response.statusCode));
                var json = JSON.parse(body);
                for (var j = 0; j < 10; j++) {
                    if (matchData.championID[indexIter] == json['participants'][j].championId) {
                        return callback(null, json['participants'][j]);
                }
            }
        });
    }
], callback); 

函数getIndividualMatchJSONObj（matchData）{ var matchParticipantData={ 具体参与者数据：[游戏数量] }; 对于（var i=0；i

---

}

在getIndividualMatchJSONObj中

for (var i = 0; i < numberOfGames; i++) {
       getIndividualMatchJSONObjHelper(matchData, matchParticipantData, i, function(err, json) {
            matchParticipantData.specificParticipantData[i] = json;
       });
} 
return matchParticipantData;

用法：

var data = test();
console.log(data);

test(function(data) {
    console.log(data);
});

回调：

function test(callback) {
    callback("test");
}

用法：

var data = test();
console.log(data);

test(function(data) {
    console.log(data);
});