This is an example of how to implement a Ephemeris Calculator for the JPL Ephemeris. The main part of the code is in de405.js. This implementation is for DE405, and I have included data only for Julian Dates 2458832.5 to 2466160.5 (Dec 15, 2019 to Jan 7, 2040). I also have a page of Test Vectors for the test data provided by the JPL for that date range.