The mobile Memento JS (JavaScript) engine (Rhino) uses a very old JS version. Add a setting allowing selection of Rhino or Google's V8.
A proposed setting to use the (current) Rhino, Google V8, or other (like Graal) JavaScript engine in place of the VERY OLD one we have now.
You see, the mobile Memento JS (JavaScript) engine (Rhino) uses a VERY OLD JS version, resulting in various things that run FINE IN THE DESKTOP EDITION and NOT IN THE MOBILE EDITION. Please add a setting to the mobile edition allowing selection of Rhino or the Google's V8 JS engine (https://v8.dev/docs/embed) or the Graal JS engine (https://www.graalvm.org/reference-manual/js/RunOnJDK/).

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Tony G commented
Rhino was deprecated years ago. It's replacement, Nashorn, has even come and gone. Nashorn is available as an addin. But I believe the Graal JS engine would be the best switchable alternative to V8.
Ref : https://en.wikipedia.org/wiki/Nashorn_(JavaScript_engine) -
Bill Crews commented
See my discussion with Ernst & maybe others to come in the forum regarding the pros & cons of having a setting versus a simple move to a new, modern JavaScript engine for mobile Memento.