Question: How to handle Date object in native C?

[weixiongmei]

Hi, I'm having hard time to figure out how to get the Date.year, month, date in the native C code. Also having hard time to figure out how to return a Date object from native to javascript. Thanks

Javascript

let date = native_driver_gui_calendar.setTodayDate(new Date(2020, 6, 10));

Native C

static jerry_value_t function_native_driver_gui_calendar_setTodayDate(const jerry_value_t func_value, /**< function object */
                                 const jerry_value_t this_value, /**< this arg */
                                 const jerry_value_t args[],    /**< function arguments */
                                 const jerry_length_t args_cnt)  /**< number of function arguments */
{
  //How to get the year, month, date of a Date object?
  //The following code returns all zero
  printf("Year:%d Month:%d Day:%d\n", ecma_date_year_from_time(args[0]), ecma_date_month_from_time(args[0]), ecma_date_date_from_time(args[0]));

 //How to return "new Date(2020, 0,0)" value to the javascript?
  return jerry_create_date();
}

[rerobika]

Hello @weixiongmei !

Unfortunately, currently we do not have any API functions to handle date objects.
Also the reason is why the the called ecma level functions are not working, it that these methods expect an ecma_number_t instead of a jerry_value_t. If you unpack it into a double variable with jerry_get_number_from_value(args[0]) you can use these internal methods, with the warning of the usage of non-api functions is not the best practice.

Moreover I can suggest you two better solutions:
A:

• ecma_date_year_from_time(args[0]) is almost equivalent to perform Date.prototype.getYear.call(args[0])
• .call() can be performed with jerry_invoke_function with args[0] as this argument
• getYear is the property of Date.prototype
• Date.prototype is the property of Date
• Date is the property of the global object.
• So putting the pieces together, use jerry_get_property (global, "Date"), then jerry_get_property(Date, "prototype"), then jerry_get_property(Date.prototype, "getYear") and finally jerry_invoke_function (Date.prototype.getYear, args[0], NULL, 0)

B:

• If you have free-time/capacity it'd be great to publish these internal method to the API. I think we should have one single universal function for retrieving information form a date object. So my proposal would look like this:

typedef enum
{
  JERRY_DATE_OPERATION_GET_YEAR,
  JERRY_DATE_OPERATION_GET_MONTH,
  // ... and so on
} jerry_date_operation_t;

jerry_value_t
jerry_date_get (jerry_date_operation_t operation, jerry_value_t value)
{
  // step 1: validate date object
  
  // step 2: get the internal date
  ecma_number_t date_num = get_the_stored_internal_date_value() // see ecma_builtin_date_prototype_dispatch_routine
  ecma_number_t result;
  // step 3: choose the operation
  switch (operation) {
    case JERRY_DATE_OPERATION_GET_YEAR: {
      result = ecma_date_year_from_time (date_num);
      break;
    }
    case JERRY_DATE_OPERATION_GET_MONTH: {
      result = ecma_date_month_from_time (date_num);
      break;
    }

   // ... and so on
  }

  return ecma_make_number_value (result);
}

Both options are suitable for resolve your problem, but IMHO the option B would be more future-proof also much efficient as well.

[weixiongmei]

@rerobika Thank you so much~~