Suggestions:
Mention the j=1 that caused the first option to disappear. Changing this to j=0 is a solution which could be mentioned in the post.
Line 20
Trigger a "change" click on the original select element to improve compatibility.
Lines 2:5 & Line 44
var x, i, j, selElmnt, a, b, c;
var event = new Event('change', {
bubbles: true,
cancelable: true,
});
/* Look for any elements with the class "custom-select": */
x = document.getElementsByClassName("ginput_container_select");
for (i = 0; i < x.length; i++) {
selElmnt = x[i].getElementsByTagName("select")[0];
/* For each element, create a new DIV that will act as the selected item: */
a = document.createElement("DIV");
a.setAttribute("class", "select-selected");
a.innerHTML = selElmnt.options[selElmnt.selectedIndex].innerHTML;
// adds custom classname to existing classes
x[i].setAttribute("class", x[i].getAttribute("class") + " custom-select");
x[i].appendChild(a);
/* For each element, create a new DIV that will contain the option list: */
b = document.createElement("DIV");
b.setAttribute("class", "select-items select-hide");
for (j = 0; j < selElmnt.length; j++) {
/* For each option in the original select element,
create a new DIV that will act as an option item: */
c = document.createElement("DIV");
c.innerHTML = selElmnt.options[j].innerHTML;
c.addEventListener("click", function(e) {
/* When an item is clicked, update the original select box,
and the selected item: */
var y, i, k, s, h;
s = this.parentNode.parentNode.getElementsByTagName("select")[0];
h = this.parentNode.previousSibling;
for (i = 0; i < s.length; i++) {
if (s.options[i].innerHTML == this.innerHTML) {
s.selectedIndex = i;
h.innerHTML = this.innerHTML;
y = this.parentNode.getElementsByClassName("same-as-selected");
for (k = 0; k < y.length; k++) {
y[k].removeAttribute("class");
}
this.setAttribute("class", "same-as-selected");
break;
}
}
h.click();
s.dispatchEvent(event);
});
b.appendChild(c);
}
x[i].appendChild(b);
a.addEventListener("click", function(e) {
/* When the select box is clicked, close any other select boxes,
and open/close the current select box: */
e.stopPropagation();
closeAllSelect(this);
this.nextSibling.classList.toggle("select-hide");
this.classList.toggle("select-arrow-active");
});
}
function closeAllSelect(elmnt) {
/* A function that will close all select boxes in the document,
except the current select box: */
var x, y, i, arrNo = [];
x = document.getElementsByClassName("select-items");
y = document.getElementsByClassName("select-selected");
for (i = 0; i < y.length; i++) {
if (elmnt == y[i]) {
arrNo.push(i)
} else {
y[i].classList.remove("select-arrow-active");
}
}
for (i = 0; i < x.length; i++) {
if (arrNo.indexOf(i)) {
x[i].classList.add("select-hide");
}
}
}
/* If the user clicks anywhere outside the select box,
then close all select boxes: */
document.addEventListener("click", closeAllSelect);