code: function FilerError({name, code, message, peerID, fileID}){
    // name should be the constructor function name(FilerError in this case), but I don't want to create one constructor for one error.
    this.name = name || 'UnknownError';
    this.code = code || 'ERR_UNKNOWN_ERROR';
    this.message = message || 'unknown error';
    this.peerID = peerID;
    this.fileID = fileID;
  }
docs: ------------------ Custom Error object