<!DOCTYPE html>
<html>

  <head>
    <link rel="stylesheet" href="style.css">
    <script src="script.js"></script>
  </head>

  <body>
<button type="button" onclick="loadDoc()">Load</button>
<br><br>
<table id="myTable"></table>
  </body>

</html>
// Code goes here

// Code goes here

function loadDoc() {
  var xhttp = new XMLHttpRequest();

  xhttp.open("GET", "file.xml", true);
  xhttp.send();


  xhttp.onreadystatechange = function() {
    if (this.readyState === 4 && this.status === 200) {
      xmlFunction(this.response);
    }
  };

}

function xmlFunction(xml) {
		var parser = new DOMParser();
		var xmlDoc = parser.parseFromString(xml, "text/xml");
		var table = "<tr><th>Category</th><th>Title</th><th>Subcategory</th></tr>"; //subcategory heading
		var x = xmlDoc.getElementsByTagName("ITEM");

		for (var elem of x) {
			var titles = elem.getElementsByTagName(
				"TITLE")[0].childNodes[0].nodeValue;
			var cats = elem.getElementsByTagName("CATEGORY")[0].childNodes[0].nodeValue;
			var subCats = elem.getElementsByTagName("SUBCATEGORY").length === 0 ? "..." : elem.getElementsByTagName("SUBCATEGORY")[0].childNodes[0].nodeValue;

				table += "<tr><td>" + cats + "</td><td>" + titles + "</td><td>" + subCats+ "</td></tr>";
		}
		document.getElementById("myTable").innerHTML = table;
}
/* Styles go here */

/* Styles go here */

table,
th,
td {
  border: 1px solid black;
  border-collapse: collapse;
}

th,
td {
  padding: 5px;
}
<?xml version="1.0" encoding="UTF-8"?>
<CATALOG>
	<ITEM>
		<TITLE>TITLE01</TITLE>
		<CATEGORY>CAT01</CATEGORY>
		<SUBCATEGORY>SUBCAT01</SUBCATEGORY>
		<ID>ID01</ID>
	</ITEM>
	<ITEM>
		<TITLE>TITLE02</TITLE>
		<CATEGORY>CAT02</CATEGORY>
		<SUBCATEGORY>SUBCAT01</SUBCATEGORY>
		<ID>ID02</ID>
	</ITEM>
	<ITEM>
		<TITLE>TITLE03</TITLE>
		<CATEGORY>CAT03</CATEGORY>
		<SUBCATEGORY>SUBCAT03</SUBCATEGORY>
		<ID>ID03</ID>
	</ITEM>
	<ITEM>
		<TITLE>TITLE04</TITLE>
		<CATEGORY>CAT04</CATEGORY>
		<SUBCATEGORY>SUBCAT04</SUBCATEGORY>
		<ID>ID04</ID>
	</ITEM>
	<ITEM>
		<TITLE>TITLE05</TITLE>
		<CATEGORY>CAT05</CATEGORY>
<SUBCATEGORY/>
		<ID>ID05</ID>
	</ITEM>
</CATALOG>