JS can we add a variable inside a regex?

Question

I just copied this snippets from stackoverflow for experimental code. And, it turns out I can’t put variables inside the “regex” thing.

So, is there a way to put variables inside a regex value like this one, or is that not a thing?

Var num = 8;
txt= txt.match(/.{1,3}/g).join("-");

Replace 3, with num

https://code.sololearn.com/WWc93fZ5ZllL/?ref=app

Answer 1

let three = 3;
let re = new RegExp(`.{1, ${three}}`, 'g') // = /.{1,3}/g
https://code.sololearn.com/Wog60qkMZTnt/?ref=app

Answer 2

It's not reeeeeally a thing. There is the regex constructor which takes a string, so you can build your regex string which includes variables and then pass it to the Regex cosntructor.

const regex = new RegExp(`.{1,${num}}`, "g");

But that is pretty ugly. It might be ok for one-off scripts, or in very select cases, but I don't feel good even typing it out. There is probably a better alternative!