Define a character class and reference it in RegExp literal

I have a character class that I want to use multiple times without copy-pasting it. So, turning something like:

let s = 'Hello, James_1234'
let re = /Hello, [wd-_]+/
console.log(re.test(s)) // => true

Into something more like:

let s = 'Hello, James_1234'
let legalNameChars = /[wd-_]/

let re = /Hello, @{legalNameChars}+/

Obviously the above code does not work, because that’s string interpolation syntax and is not applicable here. I am also aware that I could convert everything to strings and back—I would like to interpolate them directly in regex literals if possible.