The function returns all possible combinations of a given number represented as array.

all-combinations.js

//Based on https://stackoverflow.com/a/46880431/607608

function getComb(set, val) {
    const res = [];
    function comb(set, k, partial, pref) {
        if (!partial) partial = [];
        for (const element in set) {
            if (k > 1) {
                const set_copy = set.slice();
                set_copy.splice(element, 1);
                comb(set_copy, k - 1, partial.concat([set[element]]));
            }else {
                const nextVal = +(partial.concat(set[element]).join(''));
                res.push(nextVal);
            };
        }
    }
    comb(set.sort(), set.length);
    return res;
}
    
console.log(getComb([3,9,5,2]));