1
2/*https://www.w3schools.com/howto/howto_html_include.asp*/
3function includeHTML() {
4  var z, i, elmnt, file, xhttp;
5  /*loop through a collection of all HTML elements:*/
6  z = document.getElementsByTagName("*");
7  for (i = 0; i < z.length; i++) {
8    elmnt = z[i];
9    /*search for elements with a certain attribute:*/
10    file = elmnt.getAttribute("include-html");
11    if (file) {
12      /*make an HTTP request using the attribute value as the file name:*/
13      xhttp = new XMLHttpRequest();
14      xhttp.onreadystatechange = function() {
15        if (this.readyState == 4) {
16          if (this.status == 200) {elmnt.innerHTML = this.responseText;}
17          if (this.status == 404) {elmnt.innerHTML = "Page not found.";}
18          /*remove the attribute, and call this function once more:*/
19          elmnt.removeAttribute("w3-include-html");
20          includeHTML();
21        }
22      }
23      xhttp.open("GET", file, true);
24      xhttp.send();
25      /*exit the function:*/
26      return;
27    }
28  }
29};