code: function Migration(config, dataFile) {
      this.srcNetworkName = config.srcNetworkName;
      this.dstNetworkName = config.dstNetworkName;
      this.srcGateway = config.srcGateway;
      this.dstGateway = config.dstGateway;
      this.listingsRegistryAddress = config.listingsRegistryAddress;
      this.newListingsRegistryAddress = config.newListingsRegistryAddress;
      // this.privateKey = config.privateKey;
      this.gasMultiplier = config.gasSafetyMarginMultiplier;
      this.numConfirmations = config.numConfirmations;
  
      this.dataFile = dataFile;
  
      this.web3 = null;
      this.provider = null;
      this.contractAddress = null;
      this.account = null;
  
      this.submittedListings = [];
      this.minedListings = [];
      this.confirmedListings = [];
      this.errors = [];
  
      return this;
  }
docs: /////////////////////////////////////////////// ///////////////////////////////////////////////