I have Eclipse (PDT) 2020-03 (4.15.0) installed with JSDT too.
I have an existing PHP project with JavaScript support enabled, but included ECMAScript libraries are stuck on version 3 (1999!!).
How can I change ECMAScript included version? Thank you!
Upcoming Eclipse 2020-06 replaces old JSDT with WildWebDeveloper. This version fully support latest ECMA.