lib/offset.js
function fetchOffsets (offset, topics, cb, when) {
  if (!offset.ready) {
    if (when === -1) {
      offset.once('ready', () => offset.fetchLatestOffsets(topics, cb));
    } else if (when === -2) {
      offset.once('ready', () => offset.fetchEarliestOffsets(topics, cb));
    }
    return;
  }
  async.waterfall(
    [
      callback => {
        offset.client.loadMetadataForTopics(topics, callback);
      },
      (topicsMetaData, callback) => {
        var payloads = [];
        var metaDatas = topicsMetaData[1].metadata;
        Object.keys(metaDatas).forEach(function (topicName) {
          var topic = metaDatas[topicName];
          Object.keys(topic).forEach(function (partition) {
            payloads.push({
              topic: topicName,
              partition: partition,
              time: when
            });
          });
        });

        if (payloads.length === 0) {
          return callback(new Error('Topic(s) does not exist'));
        }

        offset.fetch(payloads, callback);
      },
      function (results, callback) {
        Object.keys(results).forEach(function (topicName) {
          var topic = results[topicName];

          Object.keys(topic).forEach(function (partitionName) {
            topic[partitionName] = topic[partitionName][0];
          });
        });
        callback(null, results);
      }
    ],
    cb
  );
}
function fetchOffsets (offset, topics, cb, when) {
  if (!offset.ready) {
    if (when === -1) {
      offset.once('ready', () => offset.fetchLatestOffsets(topics, cb));
    } else if (when === -2) {
      offset.once('ready', () => offset.fetchEarliestOffsets(topics, cb));
    }
    return;
  }
  async.waterfall(
    [
      callback => {
        offset.client.loadMetadataForTopics(topics, callback);
      },
      (topicsMetaData, callback) => {
        var payloads = [];
        var metaDatas = topicsMetaData[1].metadata;
        Object.keys(metaDatas).forEach(function (topicName) {
          var topic = metaDatas[topicName];
          Object.keys(topic).forEach(function (partition) {
            payloads.push({
              topic: topicName,
              partition: partition,
              time: when
            });
          });
        });

        if (payloads.length === 0) {
          return callback(new Error('Topic(s) does not exist'));
        }

        offset.fetch(payloads, callback);
      },
      function (results, callback) {
        Object.keys(results).forEach(function (topicName) {
          var topic = results[topicName];

          Object.keys(topic).forEach(function (partitionName) {
            topic[partitionName] = topic[partitionName][0];
          });
        });
        callback(null, results);
      }
    ],
    cb
  );
}
private helper