numero-bonito.js

function isBeatifulNumber(n, has = '4', hasnot = '9') {
    const numberAsString = n.toString();
    const hasFour = numberAsString.includes(has) === true;
    const hasNine = numberAsString.includes(hasnot) === false;

    return hasFour && hasNine;
}

const isBeatifulNumberHasThreeAndHasNotTwo = function (n) {
    return isBeatifulNumber(n, '3', '2');
};

console.log(isBeatifulNumber(42) === true);
console.log(isBeatifulNumber(49) === false);
console.log(isBeatifulNumber(5679) === false);
console.log(isBeatifulNumber(40009) === false);
console.log(isBeatifulNumber(4114) === true);
console.log(isBeatifulNumber(55) === false);
console.log(isBeatifulNumber(4006) === true);
console.log(isBeatifulNumber(4009) === false);
console.log(isBeatifulNumber(4019) === false);
console.log(isBeatifulNumber('4019') === false);
console.log(isBeatifulNumber('401') === true);
console.log(isBeatifulNumber('abc') === false);
console.log(isBeatifulNumberHasThreeAndHasNotTwo('123') === false);