include html in html

<div w3-include-html="content.html"></div>
   <script>
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;
    }
  }
}
</script>