code: async function () {
      const oThis = this
        , brandedToken = new BrandedTokenKlass({ERC20: oThis.erc20Address})
        , isTxHashOnlyNeeded = (oThis.returnType === 'txHash')
      ;
  
      const r = await brandedToken.approve(
        oThis.approverAddress,
        oThis.approverPassphrase,
        oThis.approveeAddress,
        oThis.toApproveAmount,
        isTxHashOnlyNeeded // we need this to be done in async and not to wait for the tx to get mined.
      );
  
      return Promise.resolve(r);
    }
docs: Approve
  
  @return {promise<result>}
  @private
  @ignore