JSFiddle - React, Tailwind, and code Playground

by George Berkeley

HTML

<form name="formulario">
    <select id="continentes" name="continentes" onchange="window[this.value]()">
      <option value="Ninguno">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="">Elige un país</option>
    </select>
  </form>

JavaScript

window.onload = function()
  {
	  document.formulario.paises.disabled = true;
  }
  
  
  function Ninguno()
  {
	  document.getElementById("paises").disabled = true;
	  option1 = new Option("Ninguno", "Ninguno", "", "selected");
	  document.formulario.paises.options[0] = option1;
  }

    
  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 Option("Francia", "Francia", "", "");
	  option5 = new Option("Holanda", "Holanda", "", "");
	  
	  document.formulario.paises.options[0] = option1;
	 ...