How Epoch Timestamp Conversion Works (Calculation Method)
Unix timestamps represent absolute UTC time deltas relative to January 1, 1970 00:00:00 UTC.
Epoch Seconds = Math.floor(Date.getTime() / 1,000)
Digit Length Auto-Detection
Detect input digit length: 10 digits indicates seconds; 13 digits indicates milliseconds.
Millisecond Normalization
If 10 digits, multiply by 1,000 (Seconds × 1,000 = Milliseconds).
Date Object Synthesis
Instantiate JavaScript Date(ms) to parse UTC timestamp.
ISO & Local Formatting
Format output strings into UTC ISO-8601 strings and localized browser time.