Shorten the chain to get to an getElement in Javascript

https://codereview.stackexchange.com/q/207335/120114

by samonela

HTML

<form id="forma1" action="" onsubmit="" style="margin:auto;">
    <select name="country" onchange="seleccionLocal(this.options[this.selectedIndex].value)">
    <option value="-1" >Estado</option>
  </select>
  <select name="city">
    <option value="-1" >Ciudad</option>
  </select>
</form>

JavaScript

var localidades = new Array(
  new Array("Baja California","Tijuana","Rosarito","Ensenada","Tecate","Mexicali","San Felipe"),
  new Array("Sonora","San Luis Río Colorado","Sonoita","Sásabe","Nogales","Naco","Agua Prieta"),
  new Array("Chihuahua","El Berrendo","Puerto Palomas","San Jerónimo","Ciudad Juárez","El Porvenir","Ojinaga"),
  new Array("Coahuila","Ciudad Acuña","Piedras Negras"),
  new Array("Nuevo León","Colombia"),
  new Array("Tamaulipas","Nuevo Laredo","Reynosa","Río Bravo","Nuevo Progreso","Matamoros")
);
window.addEventListener('DOMContentLoaded', function() {
	var forma = document.getElementById("forma1");
  console.log('forma', forma);
  console.log('forma.country', forma.country);

});
function seleccionLocal(selection){
  var cajon = document.getElementById("forma1").city;
  console.log('cajon (city): ',cajon);
  for(var x=0;x<localidades.length;x++){
    if(selection==localidades[x][0]){
      var cities = localidades[x];
      cajon.length = cities.length;
      for(var n=1;n<cities.length;n++){
        cajon[n] = new Option(cities[n],cities[n]);
      }
      break;
    }
  }
}
window.onload = function StartIt(){
  var cajon = document.getElementById("forma1").country;
  console.log('cajon(country): ',cajon);
  cajon.length = localidades.length+1;
  for(var x=0;x<localidades.length;x++){
    cajon[x+1] = new Option(localidades[x][0],localidades[x][0]);
  }
}