Function addYear

addYear(date?: Date, amount?: number): Date | undefined
Returns the year calculated date with the source date and the specified amount

If the target year does not have the same day (e.g. Feb 29 in a non-leap year), the result is clamped to the last day of the target month
Parameters
- Optionaldate: Date
  The date to inspect
- Optionalamount: number
  The amount to add, negative number means minus
Returns Date | undefined
the year calculated date with the source date and the specified amount
Author
David Hsing
Example
```
addYear(new Date(2023, 8, 30), 1);    // Date(2024, 8, 30)
addYear(new Date(2024, 1, 29), 1);    // Date(2025, 1, 28)
```