It will be guaranteed to run in 100 years time.
Any other language can die or have incompatibility issues. Over that timespan.
I am not convinced Node will be here in 100 years.
* assuming that the 100 years hyperbole is accepted
There's no guarantee we'll even be running programs written in C in 2123, let alone ones written in JavaScript. 100 years from now is a long time.
This is never guaranteed. How do you know that nothing will change in JS land in 10 years, much less 100? You don't, that's how.