Safari and Chrome doesn't evaluate dynamically added tag at page load

I am writing small JavaScript code which will load external js files at html page loading.

I tested 2 ways.

Case 1: Used document.write to add <script> tag. It worked for all browsers (IE, FF, Safari, Chrome, Opera).

Case 2: Used DOMElement.appendChild to add <script> tag to the <haed> element.

Only worked for IE, FF, and Opera. Did NOT work for Safari and Chrome.

In both cases, I expected new <script> tag is being inserted before <head> closing tag. So the new <script> tag is evaluated before processing <body>, and by the time window.onload is called, "success" variable should be true.

But it wasn't for Safari and Chrome.

Can anyone tell if this should or shouldn't work? Thank you.

<html>
  <head>
    <title>JavaScript loading test</title>
    <script type="text/javascript">
      var success = false;

      window.onload = function()
      {
        document.getElementById("result").innerHTML = success? "OK": "ERROR!";
      }

      // TEST CASE 1.
      // Works for all browsers.
      document.write('<script type="text/javascript" src="foo.js"></' + 'script>');

      // TEST CASE 2.
      // Only works for Opera, FireFox, Opera.
      // var scriptElem = document.createElement("script");
      // scriptElem.setAttribute("type", "text/javascript");
      // scriptElem.setAttribute("src", "foo.js");
      // var headElem = document.getElementsByTagName("head")[0];
      // headElem.appendChild(scriptElem);
    </script>
    <!-- expected new scrip tag being inserted here. -->
  </head>
  <body>
    Testing...<br/>
    <span id="result"></span>
  </body>
</html>

"foo.js" is just one line of code.

success = true;

Try this instead:

var s = document.createElement('SCRIPT');
s.charset = 'UTF-8';
s.src ='foo.js';
document.getElementsByTagName('HEAD')[0].appendChild(s);

But place this in a SCRIPT tag at the beginning of the BODY tag

At the time when your javascript is evaluated, the DOM isn't fully built, the head element is not even finished. You normally cannot access or manipulate the DOM ( getElementsByTagName and appendChild, etc. ) before the HTML page is fully loaded.

来源：https://stackoverflow.com/questions/2212532/safari-and-chrome-doesnt-evaluate-dynamically-added-script-tag-at-page-load

标签

javascript

scripting

appendchild

document.write

Safari and Chrome doesn't evaluate dynamically added <script> tag at page load