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    Function startOfDay

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

      This function returns a new Date object set to the beginning of the day (00:00:00.000) for the given date. The date remains the same while 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 00:00:00.000 of the same date, or Invalid Date if input is invalid

      // Get start of day from afternoon
      const result = startOfDay(new Date(2024, 5, 15, 14, 30, 45, 123));
      // Returns: June 15, 2024 00:00:00.000

      // Works with end of day time
      const result2 = startOfDay(new Date(2024, 5, 15, 23, 59, 59, 999));
      // Returns: June 15, 2024 00:00:00.000

      // Works with timestamps
      const timestamp = Date.now();
      const result3 = startOfDay(timestamp);
      // Returns: Start of today (00:00:00.000)

      // Handles month boundaries
      const result4 = startOfDay(new Date(2024, 5, 30, 15, 30));
      // Returns: June 30, 2024 00:00:00.000

      // Invalid inputs return Invalid Date
      const result5 = startOfDay(new Date("invalid"));
      // 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)
      • Preserves the date while resetting hours, minutes, seconds, and milliseconds to 0

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