index.js
function addChildren(newData) {
    var promises = [];
    newData.forEach(function (child) {
      promises.push(add(child));
    });

    return Promise.all(promises).then(emitValue);
  }
function addChildren(newData) {
    var promises = [];
    newData.forEach(function (child) {
      promises.push(add(child));
    });

    return Promise.all(promises).then(emitValue);
  }
add children to data buffer, and emit value

@return {Promise}