text: function concat(arrays) {
    // sum of individual array lengths
    let totalLength = arrays.reduce((acc, value) => acc + value.length, 0);
  
    if (!arrays.length) return null;
  
    let result = new Uint8Array(totalLength);
  
    // for each array - copy it over result
    // next array is copied right after the previous one
    let length = 0;
    for(let array of arrays) {
      result.set(array, length);
      length += array.length;
    }
  
    return result;
  }
  