Untitled

<html>
<head>
	<title></title>
	<script type="text/javascript">

		let valuesCombo =[["Ensalada", "Provoleta", "Empanadas"],
						  ["Pizza", "Ravioles", "Bife con fritas"],
						  ["Flan", "Ensalada de Frutas", "Helado"]]
		let select = document.getElementById("selectPlatos");
		let selectRng = document.getElementById("selectRng");

		selectRng.style.display = 'none'

		select.addEventListener("change", function() {
			selectRng.style.display = 'block'

			agregarCombo(valuesCombo[this.selectedIndex])

			selectRng.removeAll()
		});

		function agregarCombo(values){

			while (selectRng.firstChild) {
			  selectRng.removeChild(selectRng.firstChild);
			}

			for (var i = 0; i < values.length; i++) {
				var option = document.createElement("option")
				option.value = values[i].toLowerCase();
				option.innerHTML = values[i];

				selectRng.append(option);
			}
		}

	</script>
</head>
<body id="body">
	<form id="formulario">
		<select id="selectPlatos">
			<option value="0">Entrada</option>
			<option value="1">Plato Principal</option>
			<option value="2">Postre</option>
		</select>
		<select id="selectRng">
		</select>
		<div>

		</div>
	</form>
</body>
</html>