JSFiddle - React, Tailwind, and code Playground

by George Berkeley

HTML

<form name="formulario">
    <select id="continentes" name="continentes" onchange="actualizar()">
      <option value="null">   Elige un Continente</option>
      <option value="Africa"> África </option>
      <option value="America">América</option>
      <option value="Europa"> Europa </option>
    </select>

    <select id="paises" name="paises">
      <option value="null">Elige un país</option>
    </select>
  </form>

JavaScript

window.onload = function()
  {
	  document.formulario.paises.disabled = true;
  }
  
  
  
  function actualizar()
  {
	  var indices = document.formulario.continentes.selectedIndex;

	  switch (indices)
	  {
		  case (0): document.getElementById("paises").disabled = true;
		  break;
	
		  case (1): africa();
		  break;
	
		  case (2): america();
		  break;
	
		  case (3): europa();
		  break;
		  
		  default: alert("Error!");
		  break;
	  }
  }
  
  function africa()
  {
	  document.getElementById("paises").disabled = false;
	  
	  option1 = new Option("Angóla", "Angola", "", "");
	  option2 = new Option("Etiopía", "Etiopía", "", "");
	  option3 = new Option("Sudáfrica", "Sudafrica", "", "selected");
	  option4 = new Option("Namibia", "Namibia", "", "");
	  option5 = new Option("Gabón", "Gabón", "", "");
	  
	  document.formulario.paises.options[0] = option1;
	  document.formulario.paises.options[1] = option2;
	  document.formulario.paises.options[2] = option3;
	  document.formulario.paises.options[3] = option4;
	  document.formulario.paises.options[4] = option5;
  }

  function america()
  {
	  document.getElementById("paises").disabled = false;
	  
	  option1 = new Option("Canadá", "Canada", "", "");
	  option2 = new Option("EUA", "EUA", "", "");
	  option3 = new Option("Argentina", "Argentina", "", "");
	  option4 = new Option("Uruguay", "Uruguay", "", "");
	  option5 = new Option("Brasil", "Brasil", "", "selected");
	  
	  document.formulario.paises.options[0] = option1;
	  document.formulario.paises.options[1] = option2;
	  document.formulario.paises.options[2] = option3;
	  document.formulario.paises.options[3] = option4;
	  document.formulario.paises.options[4] = option5;
  }

  function europa()
  {
	  document.getElementById("paises").disabled = false;
	  
	  option1 = new Option("Grecia", "Grecia", "", "");
	  option2 = new Option("Alemania", "Alemania", "", "selected");
	  option3 = new Option("Inglaterra", "Inglaterra", "", "");
	  option4 = new...