formatValue(date) {
      return this.getFormat().format(date);
    }
Formats a Java Script date object into a string representing a locale date
according to the <code>formatPattern</code> property of the DatePicker instance
@public
@method
@name sap.ui.webc.main.DatePicker#formatValue
@param {Date} date A Java Script date object to be formatted as string
@returns {string} The date as string