code: function (on, joinType, table, tableAlias) {
              this.__on = on;
              this._super(arguments, [joinType, table, tableAlias]);
          }
docs: @lends patio.sql.JoinOnClause.prototype 
  Represents an SQL JOIN clause with ON conditions. Created by {@link patio.Dataset} join methods.
  See {@link patio.sql.JoinClause} for other argument parameters.
  @constructs
  @augments patio.sql.JoinClause
  
  @param on the expression to filter with. See {@link patio.Dataset#filter}
  @property on <b>READ ONLY</b> the filter to use with joining the datasets.