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

问题

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;

回答1:

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

回答2:

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