Create a string of random numbers seperated by your mask

random.js

// simply returns a  single random number
const singleRandom = function singleRandom() {
    return (Math.random() * 10).toFixed(0);
};

/*
  accept a mask of seperators, e.g. / or //::
  and return the mask strings surrounded by numbers.
  - if the seperator changes, add a space
  - / becomes X/Y
  - //:: becomes X/Y/Z A:B:C
*/
const makeRandom = function makeRandom(mask) {
    /*
        mask will be some characters, e.g. / or //::
        split this, and insert a random character between each one.
        if the mask chracter changes, add a space
        e.g. 1/2/3 4:5:6
    */
    const arr_mask = mask.split('');
    const cnt_mask = arr_mask.length;
    if (cnt_mask) {
        const new_string = [];
        let current_mask = '';
        for (let i = 0; i < cnt_mask; i += 1) {
            const next_mask = arr_mask[i];
            if (next_mask !== current_mask) {
                new_string.push(` ${singleRandom()}`);
                current_mask = next_mask;
            }
            new_string.push(current_mask + singleRandom());
        }
        // return singleRandom() + arr_mask.map(item => item + singleRandom()).join('');
        return new_string.join('');
    }

    return singleRandom();
};