Simple age calculator in JavaScript (I use it in some about-me HTMLs)

gistfile1.js

function calcAge(year, month, day) {
    const now = new Date();
    let age = now.getFullYear() - year;
    const mdif = now.getMonth() - month + 1; // jan is 0 in getMonth
    if (mdif < 0) {
        // not birthday yet
        --age;
    }
    else if (mdif === 0) {
        // maybe birthday?
        var ddif = now.getDate() - day;
        if (ddif < 0) --age; // not birthday yet
    }
    return age;
}

yes! i had to add a an else if to check for the month.
https://github.com/bennami/js-complete-course/blob/master/04-dates/03-age-by-select/script.js