editor.js
function category_changed(select){
let selected = (select.value || select.options[select.selectedIndex].value);
if (selected=='_new_'){
document.getElementById("new_category_box").style.display = "block";
} else {
document.getElementById("new_category_box").style.display = "none";
}
let catUrl = '/'+selected+'/';
document.getElementById('article_category_url').innerText = catUrl;
}
function category_added(){
let box = document.getElementById("new_category_box");
let new_category = document.getElementById("new_category_input").value;
let select = document.getElementById("category_selector");
var newOption = document.createElement("option");
newOption.value = new_category;
newOption.text = new_category;
select.add(newOption);
select.value = new_category;
category_changed(select);
box.style.display = 'none';
}