How to set up consition that all elements of one arrays must be equal to at least one element of the another array in JavaScript?

Question

Transforming roman numerals into numbers, A user enter his one roman number. and the code transfers his/her roman number into classic number.

var roman = prompt("Enter roman number", roman);
var romandigits = roman.toString().split(""); // spliting roman number entered into an array!
let romannumerals = ["M", "D", "C", "L", "X", "V", "I"];

Now condition that suppose to be set is: ALL elements of the array romandigits have to be equal to AT LEAST one element of the array romannumerals!

Answer 1

You can create a set of romannumerals

let numeralSet = new Set(romannumerals);

Then you can check that each digit is in that set

let badDigits = romanDigits.filter((c) => !numeralSet.has(c))

and then check whether there are any badDigits:

if (badDigits.length) {
    console.error(`Invalid roman number ${roman} contains non-digits ${badDigits}`);
}

So putting it all together

let roman = prompt("Enter roman number");
let romandigits = [...roman];
let romannumerals = ["M", "D", "C", "L", "X", "V", "I"];
let numeralSet = new Set(romannumerals);
let badDigits = romandigits.filter((c) => !numeralSet.has(c))
if (badDigits.length) {
    console.error(`Invalid roman number ${roman} contains non-digits ${badDigits}`);
} else {
    console.log(`${roman} is OK`);
}