如何设置变量异步瀑布?

function getIndividualMatchJSONObjHelper(matchData, matchParticipantData, indexIter, callback) {
    var individualMatchURL = 'https://na1.api.riotgames.com/lol/match/v3/matches/' + matchData.matchID[indexIter] + '?api_key=' + API_KEY;
    async.waterfall([
        function (callback) {
            request(individualMatchURL, function (err, response, body) {
                // always trigger the callback even when you have errors or else your program will hang
                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) {
                        // match found: send back data
                        console.log('inside', json['participants'][j]);
                        return callback(null, json['participants'][j]);
                    }
                }
                // if it reaches this point, no match was found
                callback();
            });
        }
    ], callback); // note: this outer 'callback' is NOT the same as the inner 'callback'
}

然后当你调用你的函数,例如。

getIndividualMatchJSONObjHelper(data, participants, indexIter, function (err, json) {
     // you can only get the JSON at this point
     console.log('outside', json);
     matchParticipantData.specificParticipantData[i] = json;
});