code: function getLengthOfCombinedArrays(name) {
      let length = 0;
      let arraySpec;
      for (let ii = 0; ii < arrayOfArrays.length; ++ii) {
        const arrays = arrayOfArrays[ii];
        const arrayInfo = arrays[name];
        const array = getArray(arrayInfo);
        length += array.length;
        if (!arraySpec || arrayInfo.data) {
          arraySpec = arrayInfo;
        }
      }
      return {
        length: length,
        spec: arraySpec,
      };
    }
docs: compute length of combined array and return one for reference