you should be aware that the icalendar specification RFC5545 clearly states in the TZID, that:
This document does not define a naming convention for time zone identifiers. Implementers may want to use the naming conventions defined in existing time zone specifications such as the public-domain TZ database [TZDB]. The specification of globally unique time zone identifiers is not addressed by this document and is left for future study.
so clearly while America/Toronto
is listed in Olsson database (see here), America/Eastern
is not which explains why your JS library cannot recognize it.
For a robust design you would need to either convert on server side to UTC or to have an actual JS class capable to parse ICS VTIMEZONE
component.