Can I use class in the custom module and constructor? It seems to be throwing the error.

you should be able to in SS2.1

That's what I thought too but it throwing an error on the constructor..

could be a syntax error. does the following work ok?

class mycustomclass{
    constructor(variable)
    {
        this.variable = variable
    }
    report()
    {
        log.debug({
            title: "report",
            details: this.variable
        })
    }
}
let instance = new mycustomclass('hello');
instance.report()

if you're using typescript, syntax errors aren't really a thing

I am not using TS.

Typescript would have given you a clear error on that code and saved you whatever time you spent before asking here, plus the time spent here on this forum. 🙂

Your efforts to drive me towards TypeScript are working 😄

heh, just pointing out some TS benefits. I do admit I occasionally have to spend some time getting my 'types' right where I wouldn't have to in plain JS, but the end result is more solid code, so I think the tradeoff is well worth it so far.

private fields/methods will work fine in SS2.1, right?

private as in hashed (#)? I don't know - haven't tried but I think that's newer than ES2019 which is what I heard SS2.1 supports. Worth a try - let us know if it works

# does not work in NS.

bummer, but not surprising. Perhaps when the update to ES2020 or whatnot?

But I assumed that everything JS should now be supported. Well...anyway.

JS changes are 'standardized' individually now, so it's difficult to know exactly which features are or are not supported by a given runtime unless an exhaustive list is made available.