code: function ContractFactory(config) {
        _classCallCheck(this, ContractFactory);
  
        this._config = config;
        this._web3 = config.web3;
        this._account = config.account;
        this._gas = config.gas;
      }
docs: Constuct a new instance.
  
  @param {Object} config Configuration.
  @param {Object} config.web3 A `Web3` instance.
  @param {Object} config.account Address of account to send transactions from.
  @param {Number} config.gas Gas amount to use for calls.