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    Function addSeconds

    • Add the specified number of seconds to the given date.

      This function validates arguments before processing and returns a new Date instance with the specified number of seconds added. Fractional seconds are truncated toward zero. Preserves milliseconds.

      Parameters

      • date: number | Date

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

      • amount: number

        The number of seconds to add (can be negative to subtract)

      Returns Date

      A new Date object with the seconds added, or Invalid Date if any input is invalid

      // Add positive seconds
      const result = addSeconds(new Date(2020, 0, 1, 12, 30, 30), 15);
      // Returns: 2020-01-01T12:30:45

      // Subtract seconds (negative amount)
      const result = addSeconds(new Date(2020, 0, 1, 12, 30, 30), -15);
      // Returns: 2020-01-01T12:30:15

      // Fractional amounts are truncated
      const result = addSeconds(new Date(2020, 0, 1, 12, 0, 0), 1.9);
      // Returns: 2020-01-01T12:00:01 (1.9 truncated to 1)

      // Crossing minute boundary
      const result = addSeconds(new Date(2020, 0, 1, 12, 30, 45), 30);
      // Returns: 2020-01-01T12:31:15

      // Invalid inputs return Invalid Date
      const result = addSeconds(new Date("invalid"), 30);
      // Returns: Invalid Date
      • Validates arguments before conversion (consistent with library patterns)
      • Accepts both Date objects and numeric timestamps
      • Fractions are truncated using Math.trunc (1.9 → 1, -1.9 → -1)
      • Preserves milliseconds
      • Returns Invalid Date for: Invalid Date, NaN, Infinity, -Infinity
      • Always returns a new Date instance (does not mutate input)

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