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    Function startOfYear

    • Get the start of the year for the given date.

      This function returns a new Date object set to January 1st at 00:00:00.000 of the same year for the given date. The year remains the same while the month is set to January (0), the day to 1, and all time components are reset to zero.

      Parameters

      • date: number | Date

        The base date as a Date object or timestamp (number)

      Returns Date

      A new Date object set to January 1st at 00:00:00.000, or Invalid Date if input is invalid

      // Get start of year from mid-year
      const result = startOfYear(new Date(2024, 5, 15, 14, 30, 45));
      // Returns: January 1, 2024 00:00:00.000

      // Works with last day of year
      const result2 = startOfYear(new Date(2024, 11, 31, 23, 59, 59));
      // Returns: January 1, 2024 00:00:00.000

      // Works with timestamps
      const timestamp = Date.now();
      const result3 = startOfYear(timestamp);
      // Returns: January 1st of current year at 00:00:00.000

      // Handles leap years
      const result4 = startOfYear(new Date(2024, 1, 29));
      // Returns: January 1, 2024 00:00:00.000

      // Invalid inputs return Invalid Date
      const result5 = startOfYear(Infinity);
      // Returns: Invalid Date
      • Validates arguments before processing (consistent with library patterns)
      • Accepts both Date objects and numeric timestamps
      • Returns Invalid Date for: Invalid Date, NaN, Infinity, -Infinity
      • Always returns a new Date instance (does not mutate input)
      • Sets month to 0 (January), day to 1, and resets hours, minutes, seconds, and milliseconds to 0

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