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    Function subMilliseconds

    • Subtract the specified number of milliseconds from the given date.

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

      Parameters

      • date: number | Date

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

      • amount: number

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

      Returns Date

      A new Date object with the milliseconds subtracted, or Invalid Date if any input is invalid

      // Subtract positive milliseconds
      const result = subMilliseconds(new Date(2020, 0, 1, 12, 0, 0, 500), 300);
      // Returns: 2020-01-01T12:00:00.200

      // Add milliseconds (negative amount)
      const result = subMilliseconds(new Date(2020, 0, 1, 12, 0, 0, 200), -300);
      // Returns: 2020-01-01T12:00:00.500

      // Fractional amounts are truncated
      const result = subMilliseconds(new Date(2020, 0, 1, 12, 0, 0, 100), 1.9);
      // Returns: 2020-01-01T12:00:00.099 (1.9 truncated to 1)

      // Crossing second boundary backward
      const result = subMilliseconds(new Date(2020, 0, 1, 12, 0, 1, 0), 1);
      // Returns: 2020-01-01T12:00:00.999

      // Invalid inputs return Invalid Date
      const result = subMilliseconds(new Date("invalid"), 500);
      // 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)
      • Returns Invalid Date for: Invalid Date, NaN, Infinity, -Infinity
      • Always returns a new Date instance (does not mutate input)

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