how-old gives how old from birthdate to any date. Not just previous dates from birthdate.
Examples
Example 1 - One day before birthday
new Date(2019, 1, 2), new Date(2020, 1, 1);{ years: 0, months: 11, days: 30 }Example 2 - On birthday
new Date(2019, 1, 2), new Date(2020, 1, 1);{ years: 0, months: 11, days: 30 }Example 3 - One day after birthday
new Date(2019, 1, 2), new Date(2020, 1, 1);{ years: 0, months: 11, days: 30 }