The base date as a Date object or timestamp (number)
A new Date object truncated to the start of the hour, or Invalid Date if input is invalid
// Basic truncation
const result = truncHour(new Date(2024, 5, 15, 14, 30, 45, 123));
// Returns: June 15, 2024 14:00:00.000
// Already at start of hour
const result2 = truncHour(new Date(2024, 5, 15, 14, 0, 0, 0));
// Returns: June 15, 2024 14:00:00.000 (unchanged)
// Works with timestamps
const timestamp = Date.now();
const result3 = truncHour(timestamp);
// Returns: Date at XX:00:00.000 of current hour
// End of hour
const result4 = truncHour(new Date(2024, 5, 15, 14, 59, 59, 999));
// Returns: June 15, 2024 14:00:00.000
// Invalid inputs return Invalid Date
const result5 = truncHour(new Date("invalid"));
// Returns: Invalid Date
Truncate a date to the start of the hour.
This function sets the minutes, seconds, and milliseconds to 0 while keeping the same date and hour, effectively removing all time components below the hour level.