Conceptos JavaScript
Acción Comando
Atras history.go(-1);
Bucle: forEach 
Object.keys(obj).forEach(function(key,index) {
    // key: the name of the object key
    // index: the ordinal position of the key within the object 
});
Error: No module.... <script> type="module"
Exportar a PDF <script src="https://cdnjs.cloudflare.com/ajax/libs/html2pdf.js/0.10.1/html2pdf.bundle.min.js" integrity="sha512-GsLlZN/3F2ErC5ifS5QtgpiJtWd43JWSuIgh7mbzZ8zBps+dvLusV+eNQATqgA/HdeKFVgA5v3S/cIrLF7QnIg==" crossorigin="anonymous" referrerpolicy="no-referrer"/>
var element = document.getElementsByTagName('html');
html2pdf(element[0]);
Fichero, leer 
var request = new XMLHttpRequest();
request.open("GET", "./myfile.txt", false);
request.send(null);
var returnValue = request.responseText;
Incluir html en html 
    function includeHTML() {
        elmnt = document.getElementById('w3-include-html')
        file = elmnt.getAttribute("w3-include-html");
        if (file) {
          xhttp = new XMLHttpRequest();
          xhttp.onreadystatechange = function () {
            if (this.readyState == 4) {
              if (this.status == 200) {
                elmnt.innerHTML = this.responseText;
              }
              if (this.status == 404) {
                elmnt.innerHTML = "Page not found.";
              }
            }
          };
          xhttp.open("GET", file, true);
          xhttp.send();
        }
    }
    includeHTML();
En html incluimos: <div w3-include-html="/cabecera.html"></div> <script src="/js/include.js"></script>
select 
sel = document.querySelector('#select')
sel.onclick = (event) => {
    event.preventDefault()
    alert(sel.value);
};