How to access a return value from a node script in BASH?

Let's say I have a bash script that calls a node script. I've tried to do it like this:

b.sh file:

#!/bin/bash
v=$(node app.js)
echo "$v"

app.js file:

#!/usr/bin/env node
function f() {
   return "test";
}
return f();

How do I access the value returned by the node script ("test") from my bash script ?

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