Question

I have a simple script im testing which calls a HTML file. In that html file is a div with the id "test2".

I am then trying to add content to its innerHTML but it acts like it don’t exist, even though the div shows in the browser.

This is how I have approached the idea:

<script>

function call_file(file,div_id){
var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById(div_id).innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET",file,true);
xmlhttp.send();

}

window.onload = function() {  

  file = 'test.html';
  div_id = 'test';
  call_file(file,div_id);
  document.getElementById('test2').innerHTML = 'Hi';
};
</script>
  <div id="test" class="outer""></div>

Content of “test.html”:

<div id="test2" class="inner"></div>

Why does it not find id "test2" with this error, even though i see the div with my own eyes:

Cannot set property 'innerHTML' of null 

Answer 1

You Cannot set it because it doesn’t exist, yet. You need to wait until it’s loaded.

You can do that with a callback function.

function call_file(file,div_id, callback){
var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById(div_id).innerHTML=xmlhttp.responseText;
    return callback();
    }
  }
xmlhttp.open("GET",file,true);
xmlhttp.send();

}

window.onload = function() {  

  file = 'test.html';
  div_id = 'test';
  call_file(file,div_id, function () {
   document.getElementById('test2').innerHTML = 'Hi';
  });
};