如下几个代码，为什么displayAbbreviations.js的代码没起作用，为什么没显示这个：

<!DOCTYPE html>
<html lang="en">

<head>
    <meta http-equiv="content-type" content="text/html; charset=utf-8" />
    <title>Explaining the Document Object Model</title>
    <link rel="stylesheet" type="text/css" media="screen" href="styles/typography.css" />
    <script type="text/javascript" src="scripts/addLoadEvent.js"></script>
    <script type="text/javascript" src="scripts/displayAbbreviations.js"></script>
    <script type="text/javascript" src="scripts/displayCitations.js"></script>
</head>

<body>
    <h1>What is the Document Object Model?</h1>
    <p>
        The <abbr title="World Wide Web Consortium">W3C</abbr> defines the <abbr title="Document Object Model">DOM</abbr> as:
    </p>
    <blockquote cite="http://www.w3.org/DOM/">
        <p>
function displayCitations() {
  if (!document.getElementsByTagName || !document.createElement || !document.createTextNode) return false;
// get all the blockquotes
  var quotes = document.getElementsByTagName("blockquote");
// loop through all the blockquotes
  for (var i=0; i<quotes.length; i++) {
// if there is no cite attribute, continue the loop
    if (!quotes[i].hasAttribute("cite")) continue;
// store the cite attribute
    var url = quotes[i].getAttribute("cite");
// get all the element nodes in the blockquote
    var quoteChildren = quotes[i].getElementsByTagName('*');
// if there are no element node, continue the loop
    if (quoteChildren.length < 1) continue;
// get the last element node in the blockquote
    var elem = quoteChildren[quoteChildren.length - 1];
// create the markup
    var link = document.createElement("a");
    var link_text = document.createTextNode("source");
    link.appendChild(link_text);
    link.setAttribute("href",url);
    var superscript = document.createElement("sup");
    superscript.appendChild(link);
// add the markup to the last element node in the blockquote
    elem.appendChild(superscript);
  }
}
addLoadEvent(displayCitations);
 

 A platform- and language-neutral interface that will allow programs and scripts to dynamically access and update the content, structure and style of documents. </p> </blockquote> <p> It is an <abbr title="Application Programming Interface">API</abbr> that can be used to navigate <abbr title="HyperText Markup Language"> HTML</abbr> and <abbr title="eXtensible Markup Language">XML </abbr> documents. </p> </body> </html>
function displayAbbreviations() {
  if (!document.getElementsByTagName || !document.createElement || !document.createTextNode) return false;
// get all the abbreviations
  var abbreviations = document.getElementsByTagName("abbr");
  if (abbreviations.length < 1) return false;
  var defs = new Array();
// loop through the abbreviations
  for (var i=0; i<abbreviations.length; i++) {
    var current_abbr = abbreviations[i];
    if (!current_abbr.childNodes.length < 1) continue;
    var definition = current_abbr.getAttribute("title");
    var key = current_abbr.lastChild.nodeValue;
    defs[key] = definition;
  }
// create the definition list
  var dlist = document.createElement("dl");
// loop through the definitions
  for (key in defs) {
    var definition = defs[key];
// create the definition title
    var dtitle = document.createElement("dt");
    var dtitle_text = document.createTextNode(key);
    dtitle.appendChild(dtitle_text);
// create the definition description
    var ddesc = document.createElement("dd");
    var ddesc_text = document.createTextNode(definition);
    ddesc.appendChild(ddesc_text);
// add them to the definition list
    dlist.appendChild(dtitle);
    dlist.appendChild(ddesc);
  }
  if (dlist.childNodes.length < 1) return false;
// create a headline
  var header = document.createElement("h2");
  var header_text = document.createTextNode("Abbreviations");
  header.appendChild(header_text);
// add the headline to the body
  document.body.appendChild(header);
// add the definition list to the body
  document.body.appendChild(dlist);
}
addLoadEvent(displayAbbreviations);
复制代码
function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      oldonload();
      func();
    }
  }
}