includeHTML.js

function includeHTML() {
	var z, i, elmnt, file, xhttp;
	/* Loop through a collection of all HTML elements: */
	z = document.getElementsByTagName("*");
	for (i = 0; i < z.length; i++) {
	  elmnt = z[i];
	  /*search for elements with a certain atrribute:*/
	  file = elmnt.getAttribute("w3-include-html");
	  if (file) {
		/* Make an HTTP request using the attribute value as the file name: */
		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.";}
			/* Remove the attribute, and call this function once more: */
			elmnt.removeAttribute("w3-include-html");
			includeHTML();
		  }
		}
		xhttp.open("GET", file, true);
		xhttp.send();
		/* Exit the function: */
		return;
	  }
	}
  }