Use JS

Maybe this is a 'pitch' to an invisible person.
Maybe JavaScript is just not interesting or exciting even valid to 'backend' and/or db engineers.
Maybe

Break The Language Barrier

Using JavaScript across a Frontend, API, Database and more can do wonders for a project.
Multiple language syntax details don't need to be one of the details that software developers are managing.
Need to update the Client? Use JS for the browser.
Need to update the data handling between the db & UI? Use JavaScript on the server.
Need to adjust how data is stored? JS for a datastore (mongodb).
Need to run some machine learning? Use JavaScript for that, too.
Need to build tests for an application? There are plenty of options for that too!

Master One Before Passing with Many

Surely polyglot programmers are the people we all want to be and become. But based on the bits that I'm familiar with regarding JavaScript alone (OOP and FP can both be accomplished, event-driven software, vertical scaling with child-processes or clusters, Prototypal Inheritance, managing streams of data, mongodb's mql, and more), as well as the plethora of already-put-together modules in the npm ecosystem, there is more than enough to learn and use that can provide functionality across a stack of needs.

Mastering some details about one language can allow for easier translation to other langauges - lists of data types, sync vs async, process flow, networking, file-system parsing, handling streams, cryptography, type definitions (ts), scoping, functional programming, object-oriented programming... if things like these make sense in 1 language they will probably be easier to "mind map" the similarities into other languages. If these things are not clear in 1 language, adding another language might only confuse what is going on.