I use the satellite.js library, which uses SGP4The de-facto TLE propagator for satellites in usual orbits is SGP4
https://github.com/shashwatak/satellite-js
satellite.js
A library to make satellite propagation via TLEs possible in the web. Provides the functions necessary for SGP4/SDP4 calculations, as callable javascript. Also provides functions for coordinate transforms.
The internals of this library are nearly identical to Brandon Rhode's sgp4 python library.