JavaScript Ascendant Calculator Tool

I need a lightweight JavaScript script that calculates the ascendant throughout the day with enough precision for both daily and intraday work. The two non-negotiable features are an accurate algorithm that respects true ascendant movement and clear output of every change during the chosen period (date, time stamp, sign, and degree).

You may read planetary positions from any reliable ephemeris API or embed your own tables—whichever yields millisecond-level speed without forcing users to chart anything manually. A simple browser-based UI or a clean function library is fine as long as it runs client-side, accepts date, time, and location, and returns a timeline of ascendant shifts for that day.

Please include:
• The well-commented JavaScript source
• A concise usage guide explaining inputs, assumptions, and how to extend or plug the code into other systems
• A brief note on the mathematical method so other researchers can audit or improve the logic

Security and confidentiality are important; no third-party trackers or analytics should be added. When the script returns correct ascendant breakpoints for several sample locations (we can test against Swiss Ephemeris data), the job is done.