Javascript:

function num_en_fa (str) {
    const num_fa = ["۰", "۱", "۲", "۳", "۴", "۵", "۶", "۷", "۸", "۹"];
    for (let i=0; i<10; i++) {
        str = str.replaceAll(String(i), num_fa[i]);
    }
    return str;
}