So Many Schemes

Firefox and Safari support an onload event for SCRIPT elements.  That is, you can dynamically add a new script to a page, set its onload event to fire a callback, and know when the script has been successfully loaded.  You would want to do this because when you include a bunch of new SCRIPT tags in a page, there are no guarantees in what order the browser will decide to evaluate them, thus making dependencies among the scripts difficult to resolve.  Using onload to chain the script additions is one solution to this, however, Internet Explorer doesn't seem to support onload in SCRIPT tags.  Here is a workaround:

  function importJS(src, look_for, onload) {
    var s = document.createElement('script');
    s.setAttribute('type', 'text/javascript');
    s.setAttribute('src', src);
    if (onload) wait_for_script_load(look_for, onload);
    var head = document.getElementsByTagName('head')[0];
    if (head) {
      head.appendChild(s);
    } else {
      document.body.appendChild(s);
    }
  }

  function importCSS(href, look_for, onload) {
    var s = document.createElement('link');
    s.setAttribute('rel', 'stylesheet');
    s.setAttribute('type', 'text/css');
    s.setAttribute('media', 'screen');
    s.setAttribute('href', href);
    if (onload) wait_for_script_load(look_for, onload);
    var head = document.getElementsByTagName('head')[0];
    if (head) {
      head.appendChild(s);
    } else {
      document.body.appendChild(s);
    }
  }

  function wait_for_script_load(look_for, callback) {
    var interval = setInterval(function() {
      if (eval("typeof " + look_for) != 'undefined') {
        clearInterval(interval);
        callback();
      }
    }, 50);
  }

  (function(){
    importCSS('some_stylesheet.css');
    importJS('jquery-1.2.6.js', 'jQuery', function() {
      importJS('some_script_that_uses_jquery.js');
      importJS('another_one.js', 'SomeClassOrVariableSetByTheScript',
        function() {
          importJS('a_script_that_uses_that_class_or_variable.js');
        });
    });
  })();

This entry was posted by Andrew on Sunday, November 23rd, 2008 at 4:26 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.