Checking for elements before executing js script?

Question

JavaScript

There is this piece of code

function check_date() {
        var a = year.value | 0,
            c = month.value | 0;
            var ch = document.getElementsByName('month','year');
            if (!ch) {
        console.warn('Element "' +ch + '" not found');
        return;
    }

        md = (new Date(a, c, 0, 0, 0, 0, 0)).getDate();
        a = document.getElementById("day").selectedIndex;
        set_select("day", md, 1, a)
    };

    if (document.addEventListener) {

        year.addEventListener('change', check_date, false);
        month.addEventListener('change', check_date, false);

    } else {
        year.detachEvent('onchange', check_date);
        month.detachEvent('onchange', check_date);
    }

}

When loading all pages except the registration page, an error, null, was advised to check for the presence of elements, wrote according to the model that was, but still does not work, double-checked and anyway, what am I doing wrong?

Answer 1

var empty = document.getElementsByName('not-existing-name');
console.log(empty, !!empty); 
//посмотрим что там 
//и что получится при приведении к булеву типу 
//(как в проверке if)
//[], true

how to fix?

if (!ch.length) {
  console.warn('Element "' +ch + '" not found');
  return;
}