How to remove all options from an interactive list and add new ones using Javascript?

Question

Hello, I am working on an interactive menu, in which the user chooses a sandwich and in this act appears a certain list of breads for choice. However, when I select a bread option and then another one appears the bread options of the two combos. Follow the code. HTML

    <select class="ped" id="ped" onchange="pao()">
        <optgroup label="Tradicionais"  id="pedido">
            <option value="301">301 - Super Frango</option>
            <option value="302">302 - Hamburguer</option>
            <option value="303">303 - Precheseburguer</option>
            <option value="304">304 - Eggs Burguer</option>
            <option value="305">305 - Americano</option>
            <option value="306">306 - Bauru</option>
            <option value="307">307 - Misto</option>
            <option value="308">308 - Queijo quente</option>
            <option value="309">309 - Cachorro quente</option>
        </optgroup>
        <optgroup label="Linha especial">
            <option value="310">310 - Sem noção</option>
            <option value="311">311 - Bedegueba</option>
            <option value="312">312 - Fortaleza</option>
            <option value="313">313 - Ceará</option>
            <option value="327">327 - TDB (Tudo de Bom)</option>
        </optgroup>
    </select>

Javascript

    function pao(){
var sand = document.getElementById('ped');
var p1 = document.createElement('option');
var p2 = document.createElement('option');
var p3 = document.createElement('option');

if (sand.value == 301 || sand.value == 312 || sand.value == 313) {
    p1.textContent = "Árabe";
    p2.textContent = "Bolão";
    opcpao.appendChild(p1);
    opcpao.appendChild(p2);
    sand.appendChild(opcpao);
} else if (sand.value == 302 || sand.value == 303 || sand.value == 304){
    for (var i = 0; i < p1.length; i++) {
        if (p1[i].innerHTMl == 'Árabe') {
            p1.remove(i);
        }
        for (var i = 0; i < p2.length; i++) {
            if(p2[i].innerHTMl == 'Bolão') {
                p2.remove(i);
            }   
        }                       
    }

    p1.textContent = "Árabe";
    p2.textContent = "Bola"
    opcpao.appendChild(p1);
    opcpao.appendChild(p2);
    sand.appendChild(opcpao);
}
document.body.appendChild(opcpao);
}
pao();

Answer 1

You can check if the element already exists before adding to the page. To do this (and make it easier), I suggest putting a id in the added element, for example, id="paes":

var opcpao = document.createElement('select'); // faltou incluir essa linha no código
opcpao.id = "paes";

And you can check if the element exists with:

if(document.body.querySelector("#paes")){
  document.body.querySelector("#paes").outerHTML = ''; // se existe, apaga
}

Soon the code would look like this:

function pao(){

   if(document.body.querySelector("#paes")){
       document.body.querySelector("#paes").outerHTML = '';
   }


   var sand = document.getElementById('ped');
   var opcpao = document.createElement('select');
   opcpao.id = "paes";
   var p1 = document.createElement('option');
   var p2 = document.createElement('option');
   var p3 = document.createElement('option');

   if (sand.value == 301 || sand.value == 312 || sand.value == 313) {
       p1.textContent = "Árabe";
       p2.textContent = "Bolão";
       opcpao.appendChild(p1);
       opcpao.appendChild(p2);
       sand.appendChild(opcpao);
   } else if (sand.value == 302 || sand.value == 303 || sand.value == 304){
       for (var i = 0; i < p1.length; i++) {
           if (p1[i].innerHTML == 'Árabe') {
               p1.remove(i);
           }
           for (var i = 0; i < p2.length; i++) {
               if(p2[i].innerHTML == 'Bolão') {
                   p2.remove(i);
               }   
           }                       
       }
   
       p1.textContent = "Árabe";
       p2.textContent = "Bola"
       opcpao.appendChild(p1);
       opcpao.appendChild(p2);
       
       sand.appendChild(opcpao);
   }
   document.body.appendChild(opcpao);
}
pao();

<select class="ped" id="ped" onchange="pao()">
        <optgroup label="Tradicionais"  id="pedido">
            <option value="301">301 - Super Frango</option>
            <option value="302">302 - Hamburguer</option>
            <option value="303">303 - Precheseburguer</option>
            <option value="304">304 - Eggs Burguer</option>
            <option value="305">305 - Americano</option>
            <option value="306">306 - Bauru</option>
            <option value="307">307 - Misto</option>
            <option value="308">308 - Queijo quente</option>
            <option value="309">309 - Cachorro quente</option>
        </optgroup>
        <optgroup label="Linha especial">
            <option value="310">310 - Sem noção</option>
            <option value="311">311 - Bedegueba</option>
            <option value="312">312 - Fortaleza</option>
            <option value="313">313 - Ceará</option>
            <option value="327">327 - TDB (Tudo de Bom)</option>
        </optgroup>
    </select>

Answer 2

Try something like that, maybe it’ll help you:

var myDiv = document.getElementById("myDiv");
var array = ["pao1","pao2","pao3","pao4"];

var selectList = document.createElement("select");
selectList.id = "mySelect";
myDiv.appendChild(selectList);

for(var i = 0; i < array.length; i++){
    var option = document.createElement("option");
    option.value = array[i];
    option.text = array[i];
    selectList.appendChild(option);
}

var mySelect = document.getElementById("mySelect");
mySelect.addEventListener("change", function(){
    var selindex  = this.selectedIndex;
    var value  = this.value;
    var index  = this.index;

    for(var i=0; i <= this.length; i++){
        if(value != this[i].value){
            this.options.remove(i);
        }
    }
});