function (currencyA, currencyB, callback) {
      if (typeof currencyB === 'function') {
        callback = currencyB;
        currencyB = null;
      }

      const parameters = {
        currencyPair: joinCurrencies(currencyA, currencyB)
      };

      return this._private('returnOpenOrders', parameters, callback);
    }
function (currencyA, currencyB, callback) {
      if (typeof currencyB === 'function') {
        callback = currencyB;
        currencyB = null;
      }

      const parameters = {
        currencyPair: joinCurrencies(currencyA, currencyB)
      };

      return this._private('returnOpenOrders', parameters, callback);
    }
function ( currencyA , currencyB , callback ) { if ( typeof currencyB === 'function' ) { callback = currencyB ; currencyB = null ; } const parameters = { currencyPair : joinCurrencies ( currencyA , currencyB ) } ; return this . _private ( 'returnOpenOrders' , parameters , callback ) ; }
can be called with `returnOpenOrders('all', callback)`
can be called with returnOpenOrders ( all callback )